Power semiconductor device

ABSTRACT

A problem associated with n-channel power MOSFETs and the like that the following is caused even by relatively slight fluctuation in various process parameters is solved: source-drain breakdown voltage is reduced by breakdown at an end of a p-type body region in proximity to a portion in the vicinity of an annular intermediate region between an active cell region and a chip peripheral portion, arising from electric field concentration in that area. To solve this problem, the following measure is taken in a power semiconductor device having a superjunction structure in the respective drift regions of a first conductivity type of an active cell region, a chip peripheral region, and an intermediate region located therebetween: the width of at least one of column regions of a second conductivity type comprising the superjunction structure in the intermediate region is made larger than the width of the other regions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2010-109957 filed onMay 12, 2010 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to a technology effectively applicable tocell periphery layout techniques or breakdown voltage enhancementtechniques in semiconductor devices (or semiconductor integrated circuitdevices), especially, power semiconductor devices such as power MOSFETs.

Japanese Unexamined Patent Publication No. 2008-124346 (PatentDocument 1) or U.S. Pat. No. 7,642,597 (Patent Document 2) discloses anexample of the following power MOSFET (Metal Oxide Semiconductor FieldEffect Transistor): a power MOSFET manufactured using a multi-epitaxytechnique or an epitaxy trench filling technique and having a so-calledsemi-super junction structure in which a super junction structure isintroduced up to some midpoint in a drift region. In this example, suchan impurity profile that the impurity concentration is gradually reducedfrom top to bottom is formed in a p-type column region comprising asemi-super junction structure. Electric field concentration at the lowerend portion of a trench field plate is thereby reduced to achieve ahigh-breakdown voltage characteristic and low on resistance.

Japanese Unexamined Patent Publication No. 2004-119611 (Patent Document3) discloses an example of a power MOSFET having a semi-super junctionstructure manufactured mainly using a multi-epitaxy technique. In thisexample, such an impurity profile that the impurity concentration isgradually increased from top to bottom is formed in an n-type columnregion comprising a semi-super junction structure. Degradation inbreakdown voltage due to charge unbalance between an n-type columnregion and a p-type column region is thereby reduced.

Japanese Unexamined Patent Publication No. 2008-258442 (Patent Document4) or US Patent Publication No. 2008-246079 (Patent Document 5)discloses an example of a power MOSFET having a semi-super junctionstructure manufactured mainly using a multi-epitaxy technique. In thisexample, an impurity profile high at the central part is formed in ann-type column region and a p-type column region comprising a semi-superjunction structure. Depletion at the upper and lower ends is therebyfacilitated to reduce electric field concentration at these parts.

Japanese Unexamined Patent Publication No. 2008-91450 (Patent Document6) or US Patent Publication No. 2008-237774 (Patent Document 7)discloses an example of a power MOSFET having a semi-super junctionstructure manufactured mainly using a multi-epitaxy technique. In thisexample, such an impurity profile that the impurity concentration isreduced stepwise from top to bottom is formed in an n-type column regionand a p-type column region comprising a semi-super junction structure toachieve a high-breakdown voltage characteristic and low on resistance.

Japanese Unexamined Patent Publication No. 2007-300034 (Patent Document8) or US Patent Publication No. 2008-17897 (Patent Document 9) disclosesan example of a power MOSFET having a semi-super junction structuremanufactured mainly using an epitaxy trench filling technique. In thisexample, the width of an n-type column region and a p-type column regioncomprising a semi-super junction structure is made different between topand bottom. (Specifically, the width of the lower part of the p-typecolumn region is reduced.) Diffusion of boron at the lower part of acolumn is thereby suppressed to prevent increase in on resistance.

Japanese Unexamined Patent Publication No. 2006-66421 (Patent Document10) or U.S. Pat. No. 7,420,245 (Patent Document 11) discloses an exampleof the following power MOSFET manufactured using a multi-epitaxytechnique: a power MOSFET having a so-called full-super junctionstructure (or simply referred to as “super junction structure”) in whicha super junction structure is introduced so that it penetrates a driftregion. In this example, an n-type column region and a p-type columnregion comprising a super junction structure are each divided into twosections, an upper section and a lower section. The concentration of theupper section is increased to reduce degradation in breakdown voltagedue to charge unbalance between the n-type column region and the p-typecolumn region.

[Patent Document 1]

-   Japanese Unexamined Patent Publication No. 2008-124346    [Patent Document 2]-   U.S. Pat. No. 7,642,597    [Patent Document 3]-   Japanese Unexamined Patent Publication No. 2004-119611    [Patent Document 4]-   Japanese Unexamined Patent Publication No. 2008-258442    [Patent Document 5]-   US Patent Publication No. 2008-246079    [Patent Document 6]-   Japanese Unexamined Patent Publication No. 2008-91450    [Patent Document 7]-   US Patent Publication No. 2008-237774    [Patent Document 8]-   Japanese Unexamined Patent Publication No. 2007-300034    [Patent Document 9]-   US Patent Publication No. 2008-17897    [Patent Document 10]-   Japanese Unexamined Patent Publication No. 2006-66421    [Patent Document 11]-   U.S. Pat. No. 7,420,245

SUMMARY

With respect to the drift regions of power MOSFETs and the like, thefollowing is a key challenge: restriction arising from conventionalsilicon limit is avoided and a high-breakdown voltage FET (for example,source-drain breakdown voltage of approximately 650 volts or above) withlow on resistance or the like is developed. For this purpose, variousmethods have been developed to introduce the following superjunctionstructure into a drift region: a superjunction structure in whichslab-like n-type column regions and p-type column regions of arelatively high concentration are alternately provided. There areroughly three techniques for introducing this superjunction structure:multi-epitaxy technique, trench insulating film burying technique, andepitaxy trench filling technique (trench fill technique or trenchepitaxy embedding technique).

Of these techniques, the multi-epitaxy technique in which epitaxialgrowth and ion implantation are repeated a large number of times is highin the degree of freedom of process and design. This accordinglycomplicates the process steps and thus increases costs.

The trench insulating film burying technique is such that a trench issubjected to oblique ion implantation and the trench (groove forembedding a p-type column region) is filled with a CVD (Chemical VaporDeposition) insulating film. This process is simpler; however, it isdisadvantageous by an amount equivalent to the area of the trench interms of area.

The epitaxy trench filling technique is such that: a trench is formed inan epitaxial layer (designated as “ordinary epitaxy layer” or “baseepitaxy layer”) as a base; and a column region of the oppositeconductivity type is embedded and formed there by burying epitaxialgrowth. Because of the restriction of growth conditions for the buryingepitaxial growth, it is relatively low in the degree of freedom ofdesign but it has an advantage of simple process steps.

The present inventors used simulation and the like to examine problemsassociated with the device structure and mass production of powerMOSFETs and the like obtained by the epitaxy trench filling technique,the multi-epitaxy technique, and the like. As a result, it was revealedthat these techniques involved the problem described below. Whenn-channel power MOSFETs will be taken as an example, the following takesplace also by relatively slight fluctuation in various processparameters: because of electric field concentration in the vicinity ofthe annular intermediate region between an active cell region and a chipperipheral portion, the source-drain breakdown voltage is reduced bybreakdown at an end of a p-type body region in proximity to thatportion.

The invention has been made to solve these problems.

It is an object of the invention to provide a high-breakdown voltage andlow-on resistance semiconductor device, such as a power solid stateactive element.

The above and other objects and novel features of the invention will beapparent from the description of this specification and the accompanyingdrawings.

The following is a brief description of the gist of the representativeelements of the invention laid open in this application:

An aspect of the invention laid open in this application is a powersemiconductor device having a superjunction structure in the respectivedrift regions of a first conductivity type of an active cell region, achip peripheral region, and the intermediate region between them. Inthis intermediate region, the width of at least one of column regions ofa second conductivity type comprising a superjunction structure is madelarger than the width of the other regions.

The following is a brief description of the gist of the effect obtainedby the representative elements of the invention laid open in thisapplication:

A power semiconductor device has a superjunction structure in therespective drift regions of a first conductivity type of an active cellregion, a chip peripheral region, and an intermediate region locatedbetween them. In this intermediate region, the width of at least one ofcolumn regions of a second conductivity type comprising a superjunctionstructure is made larger than the width of the other regions. As aresult, the following can be implemented in the intermediate regionwhere local charge unbalance occurs and electric field concentration isprone to occur: the depth at which the peak of an electric field comescan be shifted from the surface of a drift region to the inner partthereof.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an overall plan layout diagram of a chip upper surface in thedevice structure (basic structure: single line wide column type) of apower MOSFET as an example of a semiconductor device in a firstembodiment of the invention;

FIG. 2 is a plan layout diagram of p-type column regions in an entirechip surface, corresponding to FIG. 1;

FIG. 3 is an enlarged plan view of a chip corner portion CR in FIG. 2;

FIG. 4 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3;

FIG. 5 is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 3;

FIG. 6 is an explanatory drawing indicating the relation between chargebalance in the direction of depth and breakdown voltage in the vicinityof the wide p-type column region 9 b in FIG. 4 or FIG. 5;

FIG. 7 is a simulation result plot chart indicating the relation betweenan ordinary charge balance state (Qp=Qn) in such a superjunctionstructure as illustrated in FIG. 1 to FIG. 5 and the electric fieldstrength distribution in a drift region;

FIG. 8 is a simulation result plot chart indicating the relation betweenan ordinary charge balance state (Qp>Qn) in such a superjunctionstructure as illustrated in FIG. 1 to FIG. 5 and the electric fieldstrength distribution in a drift region;

FIG. 9 is a simulation result plot chart indicating the relation betweenan ordinary charge balance state (Qp<Qn) in such a superjunctionstructure as illustrated in FIG. 1 to FIG. 5 and the electric fieldstrength distribution in a drift region;

FIG. 10 is an explanatory drawing illustrating an advantage obtainedwhen an ordinary charge balance state (Qp≧Qn) is obtained in such asuperjunction structure as illustrated in FIG. 1 to FIG. 5;

FIG. 11 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (p-type column groove dryetching step);

FIG. 12 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (step of removing hardmask for p-type column groove dry etching);

FIG. 13 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (epitaxy trench fillingstep);

FIG. 14 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (planarization step);

FIG. 15 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (p⁻-type RESURF regionintroduction step);

FIG. 16 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (field insulating filmetching step);

FIG. 17 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (p-type body regionintroduction step);

FIG. 18 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (gate oxidation step);

FIG. 19 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (gate polysilicon filmformation step);

FIG. 20 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (gate polysilicon filmpatterning step);

FIG. 21 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (n⁺-type source regionintroduction step);

FIG. 22 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (interlayer insulatingfilm formation step);

FIG. 23 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (contact hole formationstep);

FIG. 24 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (p⁺-type body contactregion introduction step);

FIG. 25 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (aluminum metal electrodeformation step);

FIG. 26 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a first modification (double linewide column type) to a plan layout of the device structure of a powerMOSFET as an example of a semiconductor device in the first embodimentof the invention;

FIG. 27 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 26;

FIG. 28 is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 26;

FIG. 29 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a second modification (singlecoupled wide column type) to a plan layout of the device structure of apower MOSFET as an example of semiconductor device in the firstembodiment of the invention;

FIG. 30 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a third modification (double coupledwide column type) to a plan layout of the device structure of a powerMOSFET as an example of a semiconductor device in the first embodimentof the invention;

FIG. 31 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a fourth modification (single breakline wide column type) to a plan layout of the device structure of apower MOSFET as an example of a semiconductor device in the firstembodiment of the invention;

FIG. 32 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a fifth modification (single breakline wide column type with auxiliary column) to a plan layout of thedevice structure of a power MOSFET as an example of a semiconductordevice in the first embodiment of the invention;

FIG. 33 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, related to the devicestructure (basic structure: single partly high concentration columntype) of a power MOSFET as an example of a semiconductor device in asecond embodiment of the invention;

FIG. 34 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, related to a firstmodification (double partly high concentration column type) to a planlayout of the device structure of a power MOSFET as an example of asemiconductor device in the second embodiment of the invention;

FIG. 35 is an impurity distribution chart of a p-type column region 51 puniform in concentration in the direction of depth related to thesection taken along line D-D′ of FIG. 33 or FIG. 34 (the impuritydistribution of an adjacent n-type column region 10 is shown togetherfor the purpose of comparison);

FIG. 36 indicates a first example (substantially stepwise distribution)of the impurity distribution chart of a p-type column region 52 p partlyhigh in concentration in the direction of depth related to the sectiontaken along line C-C′ of FIG. 33 or FIG. 34 (the impurity distributionof an adjacent n-type column region 10 is shown together for the purposeof comparison);

FIG. 37 indicates a second example (substantially monotone increasing)of the impurity distribution chart of a p-type column region 52 p partlyhigh in concentration in the direction of depth related to the sectiontaken along line C-C′ of FIG. 33 or FIG. 34 (the impurity distributionof an adjacent n-type column region 10 is shown together for the purposeof comparison);

FIG. 38 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice in the second embodiment of the invention (the basic structure inFIG. 33 and the doping profile in FIG. 37 are taken as an example) (stepof forming first-tier n-type silicon epitaxial layer in multi-epitaxialgrowth);

FIG. 39 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice in the second embodiment of the invention (the basic structure inFIG. 33 taken as an example) (step #1 of implanting p-type impurity infirst-tier n-type silicon epitaxial layer in multi-epitaxial growth);

FIG. 40 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice in the second embodiment of the invention (the basic structure inFIG. 33 is taken as an example) (step #2 of implanting p-type impurityin first-tier n-type silicon epitaxial layer in multi-epitaxial growth);

FIG. 41 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice in the second embodiment of the invention (the basic structure inFIG. 33 is taken as an example) (at the time of multi-epitaxial growthby multi-epitaxy technique and the completion of final ionimplantation);

FIG. 42 is an explanatory drawing schematically illustrating therelation between breakdown voltage and charge unbalance observed in caseof the n-type epitaxial structure (n/n-multilayer ordinary epitaxystructure) in FIG. 44 and a common single ordinary epitaxial structure;

FIG. 43 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, related to amodification (trench gate) to the gate structure of a power MOSFET as anexample of a semiconductor device (basic structure and the like) in thefirst embodiment of the invention;

FIG. 44 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, related to the devicestructure (n/n-multilayer ordinary epitaxy type) of a power MOSFET of asemiconductor device in a third embodiment of the invention;

FIG. 45 is an explanatory drawing illustrating the relation betweencharge balance in the direction of depth and breakdown voltage in thesuperjunction in FIG. 44;

FIG. 46 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (step of patterning hard mask film forforming p-type column groove);

FIG. 47 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (p-type column groove etching step);

FIG. 48 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (epitaxy trench filling step);

FIG. 49 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (planarization step);

FIG. 50 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (p⁻-type RESURF region introduction step);

FIG. 51 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (field insulating film etching step);

FIG. 52 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET an example of a semiconductor device in the thirdembodiment of the invention (p-type body region introduction step);

FIG. 53 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (gate oxidation step);

FIG. 54 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of semiconductor device in the thirdembodiment of the invention (gate polysilicon film formation step);

FIG. 55 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (gate polysilicon film patterning step);

FIG. 56 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of semiconductor device in the thirdembodiment of the invention (n⁺-type source region introduction step);

FIG. 57 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (interlayer insulating film formation step);

FIG. 58 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (contact hole formation step);

FIG. 59 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (p⁺-type body contact region introductionstep);

FIG. 60 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4, illustrating amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (aluminum metal electrode formation step);

FIG. 61 is a column overall layout diagram (basic layout) correspondingto FIG. 2;

FIG. 62 is a column overall layout diagram in a first modification toFIG. 61;

FIG. 63 is a column overall layout diagram in a second modification toFIG. 61;

FIG. 64 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a sixth modification (narrow n-typecolumn type: #1) to a plan layout of the device structure of a powerMOSFET as an example of a semiconductor device in the first embodimentof the invention;

FIG. 65 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 64;

FIG. 66 is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 64;

FIG. 67 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3, related to a seventh modification (narrown-type column type: #2) to a plan layout of the device structure of apower MOSFET as an example of a semiconductor device in the firstembodiment of the invention;

FIG. 68 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 67;

FIG. 69 is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 67;

FIG. 70 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method (modification) for asemiconductor device in the second embodiment of the invention (thebasic structure in FIG. 33 and the doping profile in FIG. 37 are takenas an example) (step of forming first-tier n-type silicon epitaxiallayer in multi-epitaxial growth);

FIG. 71 is illustrates a device section in the wafer process (mainly bya multi-epitaxy technique) in a manufacturing method (modification) fora semiconductor device in the second embodiment of the invention (thebasic structure in FIG. 33 and the doping profile in FIG. 37 are takenas an example) (step #1 of implanting p-type impurity in first-tiern-type silicon epitaxial layer in multi-epitaxial growth);

FIG. 72 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method (modification) for asemiconductor device in the second embodiment of the invention (thebasic structure in FIG. 33 and the doping profile in FIG. 37 are takenas an example) (step of forming resist pattern for p-type impurityimplantation in second-tier n-type silicon epitaxial layer inmulti-epitaxial growth); and

FIG. 73 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method (modification) for asemiconductor device in the second embodiment of the invention (thebasic structure in FIG. 33 and the doping profile in FIG. 37 are takenas an example) (at the time of completion of p-type impurityimplantation in second-tier n-type silicon epitaxial layer inmulti-epitaxial growth and resist removal).

DETAILED DESCRIPTION Overview of Embodiments

Description will be given to representative embodiments of the inventionlaid open in this application.

1. A power semiconductor device includes: (a) a semiconductor chiphaving a first main surface where the source electrode of a power MOSFETis provided and a second main surface; (b) an active cell regionprovided substantially at the central part of the first main surface ofthe semiconductor chip, a chip peripheral region provided in theperiphery of the first main surface, and an annular intermediate regionprovided in the first main surface of the semiconductor chip between theactive cell region and the chip peripheral region; (c) a drift region ofa first conductivity type provided in the surfaces of the active cellregion, the chip peripheral region, and the annular intermediate regionon the first main surface side of the semiconductor chip; (d) a firstsuperjunction structure provided in the drift region in substantiallythe whole of the active cell region; (e) a second superjunctionstructure provided in the drift region corresponding to the annularintermediate region; and (f) a third superjunction structure provided inthe drift region corresponding to the chip peripheral region. At leastone of the multiple column regions of a second conductivity typecomprising the second superjunction structure is larger in width thanthe multiple column regions of the second conductivity type comprisingthe first superjunction structure.

2. The semiconductor device in Section 1 above further includes: (g) acell peripheral body region of the second conductivity type provided inthe surface region of the drift region in the first main surface of thesemiconductor chip in correspondence with the annular intermediateregion so that it surrounds the active cell region.

3. In the semiconductor device in Section 2 above, at least one of thecolumn regions of the second conductivity type is comprised of one ormore column regions of the second conductivity type and at least one ofthem is coupled with the cell peripheral body region.

4. In the semiconductor device in any of Sections 1 to 3 above, at leastthe one column region of the second conductivity type is larger in widththan the multiple column regions of the second conductivity typecomprising the third superjunction structure.

5. In the semiconductor device in any of Sections 1 to 4 above, thewidth of part of at least the one column region of the secondconductivity type is substantially equal to the width of the multiplecolumn regions of the second conductivity types comprising the firstsuperjunction structure.

6. In the semiconductor device in any of Sections 1 to 5 above, thecross section structure of the multiple column regions of the secondconductivity type comprising the first superjunction structure, thesecond superjunction structure, and the third superjunction structure isin a tapered shape and their lower parts are thinned.

7. The semiconductor device in any of Sections 1 to 6 above, thesemiconductor chip contains a silicon member as a principal constituentelement.

8. In the semiconductor device in any of Sections 1 to 7 above, thefirst conductivity type is n type.

9. In the semiconductor device in any of Sections 1 to 8 above, thesemiconductor chip comprises a single or complex power active device.

10. In the semiconductor device in any of Sections 1 to 9 above, thesemiconductor chip comprises a single device of planar power MOSFET.

11. The semiconductor device in Section 4 above further includes: (h) asurface RESURF region of the second conductivity type provided in thesurface region of the drift region in the first main surface of thesemiconductor chip so that it surrounds the active cell region and thecell peripheral body region and lower in impurity concentration than thecell peripheral body region.

12. A power semiconductor device includes: (a) a semiconductor chiphaving a first main surface where the source electrode of a power MOSFETis provided and a second main surface; (b) an active cell regionprovided substantially at the central part of the first main surface ofthe semiconductor chip, a chip peripheral region provided in theperiphery of the first main surface, and an annular intermediate regionprovided in the first main surface of the semiconductor chip between theactive cell region and the chip peripheral region; (c) a drift region ofa first conductivity type provided in the surfaces of the active cellregion, the chip peripheral region, and the annular intermediate regionon the first main surface side of the semiconductor chip; (d) a firstsuperjunction structure provided in the drift region in substantiallythe whole of the active cell region; (e) a second superjunctionstructure provided in the drift region corresponding to the annularintermediate region; and (f) a third superjunction structure provided inthe drift region corresponding to the chip peripheral region. At leastone of the multiple column regions of a second conductivity typecomprising the second superjunction structure includes a portion higherin impurity concentration than the multiple column regions of the secondconductivity type comprising the first superjunction structure.

13. In the semiconductor device in Section 12 above, the firstsuperjunction structure, the second superjunction structure, and thethird superjunction structure are formed by multi-epitaxial technique.

14. In the semiconductor device in Section 13 above, only its lower halfpart is high in concentration.

15. The semiconductor device in Section 13 above has such aconcentration gradient that the concentration is increased from top tobottom.

16. A power semiconductor device includes: (a) a semiconductor chiphaving a first main surface where the source electrode of a power MOSFETis provided and a second main surface; (b) an active cell regionprovided substantially at the central part of the first main surface ofthe semiconductor chip, a chip peripheral region provided in theperiphery of the first main surface, and an annular intermediate regionprovided in the first main surface of the semiconductor chip between theactive cell region and the chip peripheral region; (c) a drift region ofa first conductivity type provided in the surfaces of the active cellregion, the chip peripheral region, and the annular intermediate regionon the first main surface side of the semiconductor chip; (d) a firstsuperjunction structure provided in the drift region in substantiallythe whole of the active cell region; (e) a second superjunctionstructure provided in the drift region corresponding to the annularintermediate region; and (f) a third superjunction structure provided inthe drift region corresponding to the chip peripheral region. The driftregion of the first conductivity type includes an ordinary epitaxiallower region and an ordinary epitaxial upper region higher inconcentration than it.

17. In the semiconductor device Section 16 above, the impurityconcentration of the ordinary epitaxial upper region is such aconcentration that the column regions of the first conductivity type andthe column regions of the second conductivity type comprising the firstsuperjunction structure are substantially charge balanced.

18. A power semiconductor device includes: (a) a semiconductor chiphaving a first main surface where the source electrode of a power MOSFETis provided and a second main surface; (b) an active cell regionprovided substantially at the central part of the first main surface ofthe semiconductor chip, a chip peripheral region provided in theperiphery of the first main surface, and an annular intermediate regionprovided in the first main surface of the semiconductor chip between theactive cell region and the chip peripheral region; (c) a drift region ofa first conductivity type provided in the surfaces of the active cellregion, the chip peripheral region, and the annular intermediate regionon the first main surface side of the semiconductor chip; (d) a firstsuperjunction structure provided in the drift region in substantiallythe whole of the active cell region; (e) a second superjunctionstructure provided in the drift region corresponding to the annularintermediate region; and (f) a third superjunction structure provided inthe drift region corresponding to the chip peripheral region. At leastone distance between the multiple column regions of a secondconductivity type comprising the second superjunction structure isshorter than the distances between the column regions of the secondconductivity type comprising the first superjunction structure.

19. The semiconductor device in Section 18 above further includes: (g) acell peripheral body region of the second conductivity type provided inthe surface region of the drift region in the first main surface of thesemiconductor chip in correspondence with the annular intermediateregion so that it surrounds the active cell region.

20. In the semiconductor device in any of Sections 1 to 11 above, thefirst superjunction structure, the second superjunction structure, andthe third superjunction structure are formed by an epitaxy trenchfilling technique.

21. In the semiconductor device in any of Sections 12 to 15 above, thefirst superjunction structure, the second superjunction structure, andthe third superjunction structure are formed by a multi-epitaxialtechnique.

22. In the semiconductor device in any of Sections 16 to 19 above, thefirst superjunction structure, the second superjunction structure, andthe third superjunction structure are formed by an epitaxy trenchfilling technique.

23. In the semiconductor device in any of Sections 1 to 22 above, afield plate is provided over the annular intermediate region with aninterlayer insulating film in between.

(Explanation of Style of Description, Basic Terms, and Usage Thereof inthis Specification)

1. The description of embodiments in this specification may be dividedinto multiple sections as required for the sake of convenience. Thesesections are not independent of or separate from one another unlessotherwise explicitly stated. Each section is each part of a singleexample and one section is the details of part of another or amodification or the like to part or all of another. The repetitivedescription of a similar part will be omitted as a rule. Eachconstituent element of the embodiments is not indispensable unlessotherwise explicitly stated, the number of constituent elements istheoretically limited, or the constituent element is contextuallyobviously indispensable.

When “semiconductor device” is cited in this specification, it refers towhat is obtained by integrating mainly various transistors, singlediodes (active elements), or resistors, capacitors, and the like locatedaround them over a semiconductor chip or the like (for example, singlecrystal silicon substrate). An example of a transistor representative ofthe various transistors cited here is MISFET (Metal InsulatorSemiconductor Field Effect Transistors) typified by MOSFET (Metal OxideSemiconductor Field Effect Transistor). Examples of transistorsrepresentative of various single transistors are power MOSFET and IGBT(Insulated Gate Bipolar Transistor). The IGBT cited here is a bipolartransistor with a power MOSFET incorporated therein and they arebasically classified according to the power MOSFETs incorporatedtherein.

The power MOSFETs (basically the same with the IGBTs) are roughlyclassified into vertical type and lateral type. The vertical powerMOSFETs and the like can be further classified into planar type andtrench type. In this specification, planar power MOSFET and trench powerMOSFET will be concretely described.

2. Even when the wording of “X comprised of A” or the like is used inthe description of the embodiments or the like with respect to material,composition, or the like, what containing an element other than A as oneof major constituent elements is not excluded. This applies unlessotherwise explicitly stated or it is contextually obviously excluded.Examples will be taken. With respect to component, the above wordingmeans that “X including A as a main component” or the like. A term of“silicon member” or the like is not limited to members of pure siliconand includes SiGe alloys, other multi-element alloys predominantlycomposed of silicon, and members containing other additive or the like,needless to add. Similarly, even when the term of “silicon oxide film,”“silicon oxide insulating film,” or the like is used, it does notinclude only relatively pure undoped silicon dioxide. It also includesthe following, needless to add: thermally-oxidized films of FSG(Fluorosilicate Glass), TEOS-based silicon oxide, SiOC (SiliconOxicarbide) or carbon-doped silicon oxide or OSG (Organosilicate glass),PSG (Phosphorus Silicate Glass), BPSG (Borophosphosilicate Glass), orthe like; CVD oxide films; silica low-k insulating films (porousinsulating films) obtained by introducing electron holes in a member ofapplied silicon oxide, such as SOG (Spin ON Glass), NCS (Nano-ClusteringSilica), or the like or a similar member; composite films with any othersilicon insulating film containing them as a principal constituentelement; and the like.

As silicon insulating films regularly used in the field of semiconductoralong with silicon oxide insulating films, there are silicon nitrideinsulating films. The materials belonging to this family include SiN,SiCN, SiNH, SiCNH and the like. When the term of “silicon nitride” isused here, it includes both SiN and SiNH unless otherwise explicitlystate. Similarly, when the term of “SiCN” is used, it includes both SiCNand SiCNH unless otherwise explicitly state.

SiC has similar properties to those of SiN. SiON should be oftenclassified into silicon oxide insulating film.

3. In the following description, preferred examples are taken withrespect to graphic, position, attribute, or the like. However, theinvention should not be strictly limited to such examples unlessotherwise explicitly stated or it should be contextually obviouslylimited to them, needless to add.

4. When reference is made to any specific numeric value or quantity, thespecific numeric value or quantity may be exceeded or may be underrun.This applies unless otherwise explicitly stated, any other specificnumerical value or quantity is theoretically impermissible, or thespecific value or quantity contextually may not be exceeded or underrun.

5. When the term of “wafer” is used, it usually refers to a singlecrystal silicon wafer over which a semiconductor device (the same withsemiconductor integrated circuit device and electronic device) isformed. However, it also includes an epitaxial wafer, a composite waferof an insulating substrate, such as SOI substrate, LCD glass substrate,or the like, and a semiconductor layer or the like, and the like,needless to add.

6. In general, the superjunction structure refers to a structureobtained by inserting columnar or plate-like column regions of theopposite conductivity type into a semiconductor region of someconductivity type at substantially equal intervals so that chargebalance is maintained. When a “superjunction structure” by a trench filltechnique is cited in this specification, it refers to a structureobtained by taking the following measure, as a rule: plate-like “columnregions” of the opposite conductivity type are inserted into asemiconductor region of some conductivity type at substantially equalintervals so that charge balance is maintained. (Usually, the “columnregions” are in the shape of flat plate but they may be curved or bent.)In the description of embodiments, a structure formed by placing p-typecolumns in an n-type semiconductor layer (for example, a drift region)in parallel at substantially equal intervals.

Some superjunction structures are “semi-superjunction structure” inwhich p-type column regions or the like are terminated at some midpointin an n-type drift region. Meanwhile, other superjunction structures are“full-superjunction structure” in which p-type column regions or thelike penetrate an n-type drift region. The full-superjunction structureis more advantageous to the achievement of high breakdown voltage andlow on resistance. In this specification, the full-superjunctionstructure will be mainly dealt with.

When the term of “orientation” is used with respect to a superjunctionstructure, it refers to the following direction: the direction of lengthas a p-type column or an n-type column comprising the superjunctionstructure is two-dimensionally viewed in correspondence with a mainsurface of the chip (in a plane parallel to a main surface of the chipor the wafer).

When the term of junction edge extension or surface RESURF region(specifically, “p⁻-type surface RESURF region”) is used with respect toRESURF (Reduced Surface Field) structure or junction edge terminationstructure in this specification, it refers to the following region: aregion that is formed in the surface region of a drift region, coupledto an end of a p-type body region (p-type well region) comprising achannel region, and of the same conductivity type as that thereof andlower in impurity concentration than it. In general, it is formed in aring shape so that it surrounds a cell part. Field plate refers to apart of a conductor film pattern coupled to source potential orpotential equivalent thereto, that is extended to above the surface(device surface) of a drift region through an insulating film andsurrounds a cell part in a ring-like manner. Floating field ring orfield limiting ring refers to the following impurity region or impurityregion group: an impurity region or impurity region group that isprovided in the surface (device surface) of a drift region separatelyfrom a p-type body region (p-type well region), has the sameconductivity type as that thereof and a concentration similar to thatthereof, and singly or multiply surrounds a cell part in a ring-likemanner.

Details of Embodiments

Further detailed description will be given to embodiments. In eachdrawing, the same or similar parts will be marked with the same orsimilar codes or reference numerals and the description thereof will notbe repeated as a rule.

In each accompanying drawing, hatching or the like may be omitted evenfrom a section when it complicates the drawing or it is clearlydistinguishable from an airspace. Even in case of a planarly closedhole, a background contour line may be omitted when the hole is clearlyrecognizable from description or the like. Hatching may be given tosomething to clearly indicate that it is not an airspace even though itis not a section.

With respect to peripheral side regions or the like, for example, thenumber of p-type columns shown in each drawing is three or five as amatter of the convenience of diagrammatic representation. In actuality,the number may be larger than 10 or so. In the following description, asemiconductor device with a breakdown voltage of several hundred voltsor so will be taken as an example. In the following description, aproduct with a breakdown voltage of several hundred volts or so (forexample, 600 volts) will be taken as an example.

The preceding patent applications disclosed with respect to a powerMOSFET utilizing a superjunction structure are, for example, JapanesePatent Application No. 2009-263600 (filed on Nov. 19, 2009 in Japan),Japanese Patent Application No. 2010-81905 (filed on Mar. 31, 2010 inJapan), and the like.

1. Description of the Device Structure (Basic Structure: Single LineWide Column Type) of a Power MOSFET as an Example of a SemiconductorDevice in the First Embodiment of the Invention (Mainly, FIG. 1 to FIG.10)

In the following concrete description, a planar power MOSFET fabricatedin a silicon semiconductor substrate with a source-drain breakdownvoltage of 600 volts or so will be taken as an example. (With respect toplanar power MOSFETs, this is the same with the following sections.)However, the invention is also applicable to power MOSFETs and otherdevices having any other breakdown voltage value, needless to add.

FIG. 1 is an overall plan layout diagram of a chip upper surface in thedevice structure (basic structure: single line wide column type) of apower MOSFET as an example of a semiconductor device in the firstembodiment of the invention. FIG. 2 is a plan layout diagram of p-typecolumn regions in an entire chip surface, corresponding to FIG. 1. FIG.3 is an enlarged plan view of a chip corner portion CR in FIG. 2. FIG. 4is a device sectional view corresponding to the section taken along lineA-A′ of FIG. 3. FIG. 5 is a device sectional view corresponding to thesection taken along line B-B′ of FIG. 3. FIG. 6 is an explanatorydrawing indicating the relation between charge balance in the directionof depth and breakdown voltage in the vicinity of the wide p-type columnregion 9 b in FIG. 4 or FIG. 5. FIG. 7 is a simulation result plot chartindicating an ordinary charge balance state (Qp=Qn) in such asuperjunction structure as illustrated in FIG. 1 to FIG. 5 and theelectric field strength distribution in a drift region. FIG. 8 is asimulation result plot chart indicating the relation between an ordinarycharge unbalance state (Qp>Qn) in such a superjunction structure asillustrated in FIG. 1 to FIG. 5 and the electric field strengthdistribution in a drift region. FIG. 9 is a simulation result plot chartindicating the relation between an ordinary charge unbalance state(Qp<Qn) in such a superjunction structure as illustrated in FIG. 1 toFIG. 5 and the electric field strength distribution in a drift region.FIG. 10 is an explanatory drawing illustrating an advantage obtainedwhen an ordinary charge unbalance state (Qp≧Qn) is obtained in such asuperjunction structure as illustrated in FIG. 1 to FIG. 5. Descriptionwill be given to the device structure (basic structure: single line widecolumn type) of a power MOSFET as an example of a semiconductor devicein the first embodiment of the invention.

First, description will be given to the overall layout of a chip (singleor complex power active device) with reference to FIG. 1. As illustratedin FIG. 1, a guard ring 3 is provided in the peripheral portion of achip 2 (the principal part thereof is a silicon member). (The areaoutside the guard ring is the outermost peripheral p⁺-type region 7.) Agate metal electrode 4 is provided inside the guard ring. A source metalelectrode 5 occupies the central part of the chip 2 and an active cellregion 6 is formed in substantially the whole area under the sourcemetal electrode 5.

FIG. 2 is a planar structural drawing of a semiconductor substratesurface region under the source metal electrode 5 of the chip 2illustrated in FIG. 1. As illustrated in FIG. 2 (Refer to FIG. 4, FIG.5, or the like), the layout of the semiconductor chip 2 as viewed fromthe device main surface 1 a side is comprised of the following: asubstantially rectangular (square or oblong) active cell region 6located at the central part; a ring-shaped intermediate region 40surrounding it; a ring-shaped chip peripheral region 15 located furtheroutside it; and the like. (The semiconductor chip can be reworded aschip region. In this description, a chip 3 millimeters square will betaken as an example.) (The device main surface 1 a is the surface on theopposite side to the back surface 1 b of the chip 2.)

This cell region 6 is comprised of: linear repetitive gate electrodes 11as a principal part of the power MOSFET; p-type body regions 12 providedin the surface region of an n-type silicon epitaxial layer 1 n so thatthey surround them; a superjunction structure comprised of a largenumber of p-type column regions 9 (ordinary p-type column regions 9 a,identical in width); and the like. (The p-type body regions 12 includean annular p-type body region 12 p surrounding the active cell region6.) (The n-type silicon epitaxial layer 1 n is equivalent to an n-typedrift region 30, that is, a drift region of a first conductivity type.)(The above superjunction structure is equivalent to the firstsuperjunction structure 41 described with reference to FIG. 3, 4micrometers or so in column thickness and 6 micrometers or so in columnspacing.)

The following are provided on both sides of the active cell region 6 inthe annular intermediate region 40 (intermediate region): wide p-typecolumn regions 9 b and ordinary p-type column regions 9 a each havingthe same orientation as that of the first superjunction structure 41;and the like. (Both the p-type column regions 9 b and the p-type columnregions 9 a are collectively designated as p-type column regions 9 orcolumn regions of a second conductivity type). The following areprovided above and below the active cell region 6: wide p-type columnregions 9 b and ordinary p-type column regions 9 a each having anorientation orthogonal to the first superjunction structure 41; and thelike. These wide p-type column regions 9 b and ordinary p-type columnregions 9 a and the like comprise a second superjunction structure 42.

In the surface of the drift region 30 (refer to FIG. 4, FIG. 5, or thelike) of the chip peripheral region 15, there is provided an annularp⁻-type surface RESURF region 14 (usually, lower in impurityconcentration than the p-type body region 12). The p⁻-type surfaceRESURF region 14 is so provided that it is coupled with the annularp-type body region 12 p and surrounds it. (In this example, the widep-type column region 9 b is directly coupled with the annular p-typebody region 12 p.) In the areas in the chip peripheral region 15corresponding to both side of the active cell region 6 and correspondingto above and below it, the following are provided: multiple ordinaryp-type column region 9 a and the like respectively having the sameorientation as the corresponding second superjunction structure 42. Theycomprise a third superjunction structure 43. That is, the width of thep-type column regions 9 b (extraordinary p-type column regions) islarger than that of the principal ordinary p-type column regions 9 acomprising the first superjunction structure 41 and the thirdsuperjunction structure 43.

Description will be given to the details of the layout and the relationwith a vertical structure with reference to FIG. 3 illustrating the chipcorner portion CR including the upper right end portion of the cell partin FIG. 2 in an enlarged manner. In this layout under the metalelectrode, the following measure is taken: it is axisymmetric withrespect to the center lines (vertical, horizontal) of the chip and is180-degree rotationally symmetric with respect to the center of thechip. (In actual chip layout, irregular planar concavities andconvexities are often involved because of various reasons.) (Extractionelectrodes, source pads, gate pads, or the like do not necessarily havethis symmetrical property.) Therefore, when the vicinity of one corneris described, that is substantially equivalent to that substantially thewhole of the chip 2 is described. In the following description mainly ofplan layout, the vicinity of the upper right part of the chip 2 will betaken as an example. As illustrated in FIG. 3, the wide p-type columnregions 9 b coupled to the cell peripheral body region 12 psubstantially planarly surround the first superjunction structure 41.

FIG. 4 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 (the section taken along line A-A′ of FIG. 1);and FIG. 5 is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 3. As illustrated in FIG. 4 and FIG. 5, thesemiconductor substrate 1 in which this device is formed is obtained byforming an ordinary single n-type silicon epitaxial layer in over ann⁺-type single crystal silicon substrate 1 s (the back surface 1 b sideof the semiconductor substrate 1). Therefore, the n-type column regions10 are part of the silicon epitaxial layer 1 n (n-type drift region 30).A field insulating film 16 and a gate insulating film 21 are provided onthe front surface 1 a side of the semiconductor substrate 1 and apolysilicon gate electrode 11 is provided over the gate insulating film21. An interlayer insulating film 17 is provided so that it covers thefield insulating film 16 and the polysilicon gate electrode 11. In thesurface region on the front surface 1 a side of the semiconductorsubstrate 1, there is provided an n⁺-type source region 19 in aself-aligned manner with respect to the polysilicon gate electrode 11.(An n⁺-type channel stopper region 8 is usually formed at the same timeas this step.) In the surface region on the front surface 1 a side ofthe semiconductor substrate 1, there is provided a p⁺-type body contactregion 18 in correspondence with a contact hole formed in the interlayerinsulating film 17 in the vicinity of the polysilicon gate electrode 11.The outermost peripheral p⁺-type region 7 is usually formed at the sametime as this step. Further, a guard ring 3, a source metal electrode 5,and the like comprised of a barrier metal film, an aluminum metalelectrode film, or the like are formed over the interlayer insulatingfilm 17. The area ranging from the outer half part of the p-type bodyregion 12 p(12) at an end of the active cell region 6 to a field platepart 13 is the intermediate region 40. (The field plate part 13 is anelectrode kept at a source potential for reducing electric fieldconcentration in the vicinity of the surface of the drift region.) Thearea located outside the above area is the cell peripheral region 15.

FIG. 6 illustrates the electrical structure of the semiconductorsubstrate 1 (n-type drift region 30) in the vicinity of the wide p-typecolumn region 9 b in the superjunction structure in FIG. 4 and FIG. 5.As shown in FIG. 6, the total charge amount Qp of the p-type columnregion 9 b is larger than the total charge amount Qn of the adjacentn-type column regions 10 in the vicinity of the wide p-type columnregion 9 b. Therefore, the following can be implemented by long-timeheat treatment, such as burying epitaxial growth, even when the impurityconcentration of the p-type column region 9 b located below isrelatively reduced: the point at which the charge area density q of eachcolumn is substantially equal, that is, the peak of electric fieldstrength E in the drift region in the direction of depth Y can belocated in a relatively low position. The area on the left side of theline of flexure indicating the electric field strength E in FIG. 6 isequivalent to the source-drain breakdown voltage V_(B) of this portion.

FIG. 7 to FIG. 9 show results obtained by simulating the relationbetween charge balance in a superjunction structure and the electricfield strength distribution of the n-type drift region 30 in thedirection of depth. As shown in these drawings, the following can beimplemented by establishing the relation of total charge amount Qp≧totalcharge amount Qn: even when various process parameters vary, the pointat which the electric field is concentrated (that is, breakdown point)can be shifted from the surface to the internal region.

FIG. 10 shows variation in breakdown voltage and breakdown mode when thedose amount in ion implantation in the p⁻-type surface RESURF region 14varies. As shown in FIG. 10 (left side), in such a structure asillustrated in FIG. 1 to FIG. 5, the following takes place when thecharge balance in the superjunction is in the relation of total chargeamount Qp<total charge amount Qn: even with the best dose amount, thebreakdown mode is cell end-cell inside simultaneous breakdown. When thedose amount is shifted to the smaller side, the principal mode is cellend breakdown. When the dose amount is shifted to the larger side, theprincipal mode is breakdown at an end of the surface RESURF layer.

As shown in FIG. 10 (right side), meanwhile, the following takes placewhen charge balance in the superjunction is in the relation of totalcharge amount Qp≧total charge amount Qn: the breadth of the portion inwhich the principal mode is breakdown at an end of the surface RESURFlayer is unchanged; but an ideal cell inside breakdown mode can beestablished in the other broad portion.

2. Description of the Wafer Process (Mainly by Epitaxy Trench FillingTechnique) in a Manufacturing Method for a Semiconductor Device in theFirst Embodiment of the Invention (Mainly FIG. 11 to FIG. 25)

In this section, the wafer process will be described with the devicestructure described in Section 1 taken as an example. However, thisprocess is not limited to the above specific structure and can bebasically similarly applied to the follow modifications and otherembodiments with respect to corresponding portions, needless to add.

FIG. 11 is a device sectional view illustrating a process flowcorresponding to the device section in FIG. 4 (p-type column groove dryetching step). FIG. 12 is a device sectional view illustrating theprocess flow corresponding to the device section in FIG. 4 (step ofremoving hard mask for p-type column groove dry etching). FIG. 13 is adevice sectional view illustrating the process flow corresponding to thedevice section in FIG. 4 (epitaxy trench filling step). FIG. 14 is adevice sectional view illustrating the process flow corresponding to thedevice section in FIG. 4 (planarization step). FIG. 15 is a devicesectional view illustrating the process flow corresponding to the devicesection in FIG. 4 (p⁻-type RESURF region introduction step). FIG. 16 isa device sectional view illustrating the process flow corresponding tothe device section in FIG. 4 (field insulating film etching step). FIG.17 is a device sectional view illustrating the process flowcorresponding to the device section in FIG. 4 (p-type body regionintroduction step). FIG. 18 is a device sectional view illustrating theprocess flow corresponding to the device section in FIG. 4 (gateoxidation step). FIG. 19 is a device sectional view illustrating theprocess flow corresponding to the device section in FIG. 4 (gatepolysilicon film formation step). FIG. 20 is a device sectional viewillustrating the process flow corresponding to the device section inFIG. 4 (gate polysilicon film patterning step). FIG. 21 is a devicesectional view illustrating the process flow corresponding to the devicesection in FIG. 4 (n⁺-type source region introduction step). FIG. 22 isa device sectional view illustrating the process flow corresponding tothe device section in FIG. 4 (interlayer insulating film formationstep). FIG. 23 is a device sectional view illustrating the process flowcorresponding to the device section in FIG. 4 (contact hole formationstep). FIG. is a device sectional view illustrating the process flowcorresponding to the device section in FIG. 4 (p⁺-type body contactregion introduction step). FIG. 25 is a device sectional viewillustrating the process flow corresponding to the device section inFIG. 4 (aluminum metal electrode formation step). Description will begiven to the wafer process (mainly by an epitaxy trench fillingtechnique) in a manufacturing method for a semiconductor device in thefirst embodiment of the invention with reference to these drawings.

First, as illustrated in FIG. 11, a semiconductor wafer 1 in which ann-epitaxial layer 1 n, 50 micrometers or so in thickness, doped withphosphorus is formed over an n⁺-silicon single crystal substrate isdoped with antimony is prepared. (Antimony is doped to the order of, forexample, 10¹⁸ to 10¹⁹/cm³.) (In this example, the n⁺-silicon singlecrystal substrate 1 s, for example, a 200φ-wafer. The wafer diameter maybe 150φ, 300φ, or 450φ.) (In terms of device, the n-epitaxial layer inis a region to be a drift region and the concentration is, for example,3×10¹⁵/cm³ or so in phosphorus concentration.) A hard mask film 22 forforming trenches for p-type columns comprised of, for example, P-TEOS(Plasma-Tetraethylorthosilicate) or the like is formed over the devicesurface 1 a (main surface on the opposite side to the back surface 1 b)of the semiconductor wafer 1. The width Wn of the n-type column region10 at the patterning level is, for example, 6 micrometers or so and thewidth Wp of the ordinary p-type column region 9 a is, for example, 4micrometers or so. (That is, the pitch of the superjunction is 10micrometers or so.) Subsequently, the n-epitaxial layer 1 n and the likeare subjected to anisotropic dry etching with the hard mask film 22 forforming trenches for p-type columns used as a mask. (The hard mask film22 is, for example, a plasma TEOS film, a silicon nitride film, or alaminated film of them and an example of its thickness is 1.5micrometers or so.) (An example of the gas atmosphere is a mixedatmosphere of Ar, SF₆, O₂, and the like and an example of the etchingdepth is 50 micrometers or so.) Trenches 23 for p-type columns arethereby formed.

Subsequently, the hard mask film 22 that became unnecessary is removedas illustrated in FIG. 12.

Subsequently, as illustrated in FIG. 13, burying epitaxial growth iscarried out on the trenches 23 for p-type columns to form a p-typeburying epitaxial layer 24. (The boron concentration is, for example,5×10¹⁵/cm³ or so.) Examples of the source gas for burying epitaxialgrowth are silicon tetrachloride, trichlorosilane, dichlorosilane, andmonosilane. An example of the preferable range of processing atmosphericpressure is 10 kPa to 110 kPa or so.

Subsequently, as illustrated in FIG. 14, the p-type burying epitaxiallayer 24 located outside the trenches 23 for p-type columns (FIG. 13) isremoved by a planarization step, for example, CMP (Chemical MechanicalPolishing). Then the front surface 1 a of the semiconductor wafer 1 isplanarized.

Subsequently, as illustrated in FIG. 15, a silicon oxide film 16 isformed over substantially the entire front surface 1 a of thesemiconductor wafer 1 by thermal oxidation. (The silicon oxide film 16is a field oxide film and its thickness is, for example, 350 nm or so.)A resist film 25 for introducing a p⁻-type RESURF region is formedthereover by lithography. Subsequently, a p⁻-type surface RESURF region14 is introduced by ion implantation with the resist film 25 forintroduction a p⁻-type RESURF region used as a mask. (The dopant is, forexample, boron; the dose amount is, for example, 1×10¹¹ to 1×10¹²/cm² orso; and the implantation energy is, for example, 200 keV or so.)Thereafter, the resist film 25 that became unnecessary is entirelyremoved.

Subsequently, as illustrated in FIG. 16, a resist film 26 for fieldinsulating film processing is formed over the field oxide film 16 bylithography and using it as a mask, the edge portions, active cellregion 6, and the like of the chip are exposed. Thereafter, the resistfilm 26 that became unnecessary is entirely removed.

Subsequently, as illustrated in FIG. 17, a resist film 27 for p-typebody region introduction is formed over the front surface 1 a of thesemiconductor wafer 1 by lithography. Using this film as a mask, ap-type body region 12 is introduced by ion implantation (the dopant isboron). This ion implantation is carried out in two steps describedbelow, for example. At the first step, implantation is carried out at,for example, 200 keV on the order of 10¹³/cm² and at the subsequentstep, or the second step, implantation is carried out at, for example,75 keV on the order of 10¹²/cm².

According to the non-self-alignment p-type body region introductionprocess used here, the portion to be a gate electrode has been alreadyrecessed to 1 micrometer or so at the time of doping. Therefore, it ispossible to reduce the burden on the subsequent heat treatment. As aresult, it is possible to reduce unwanted variation in the impuritydistribution of the superjunction. However, as the result of the depthof the p-type body region 12 being reduced, breakdown voltage may bereduced as aside-effect. To avoid this problem, the ion implantation inthe p-type body region 12 is carried out in two steps as mentionedabove.

As mentioned above, the p-type body region 12 of the second conductivitytype is introduced before the formation of a gate polysilicon film. Thusthe introduced portion is not limited by the width or position of thegate and it can be introduced in the optimum position. This makes itpossible to reduce the burden on the subsequent heat treatment and, inaddition, use the subsequent heat treatment (including the formation ofa gate polysilicon film and the like) in a shared manner. Thisnon-self-alignment p-type body region introduction process is applicableto not only cases where the ordinary epitaxy layer as the base forsuperjunction formation is of single layer but also cases where it is ofmultilayer.

Subsequently, as illustrated in FIG. 18, agate oxide film 21 (forexample, 50 to 200 nm or so in film thickness) is formed over the frontsurface 1 a of the semiconductor wafer 1 by thermal oxidation (forexample, wet oxidation at 950 degrees Celsius).

As illustrated in FIG. 19, a gate polysilicon film 11 (for example, 200to 800 nm or so in film thickness) is formed over the gate oxide film 21by, for example, low pressure CVD (Chemical Vapor Deposition). As wafercleaning before gate oxidation, for example, wet cleaning using a firstcleaning liquid and a second cleaning liquid can be applied. The firstcleaning liquid is a liquid of ammonia:hydrogen peroxide:purewater=1:1:5 (volume ratio) and the second cleaning liquid is a liquid ofhydrochloric acid:hydrogen peroxide:pure water=1:1:6 (volume ratio).

Subsequently, as illustrated in FIG. 20, the gate electrode 11 ispatterned by dry etching.

Subsequently, as illustrated in FIG. 21, a resist film 28 for n⁺-sourceregion introduction is formed by lithography. Using this film as a mask,an n⁺-source region 19, the n⁺-type channel stopper region 8 of chipedge parts, and the like are introduced by ion implantation (forexample, arsenic). (The dopant is, for example, arsenic; the dose amountis, for example, the order of 10¹⁵/cm² or so; and the implantationenergy is, for example, 40 keV or so.) Thereafter, the resist film 28that became unnecessary is entirely removed.

Subsequently, as illustrated in FIG. 22, a PSG (Phospho-Silicate-Glass)film 17 (interlayer insulating film) is formed over substantially theentire front surface 1 a of the semiconductor wafer 1 by CVD or thelike. (An SOG film may be stacked above and planarized.) As theinterlayer insulating film 17, aside from the PSG film, BPSG, TEOS film,SiN film, others, or a composite film of them can be applied. An exampleof the total film thickness of the interlayer insulating film 17 is 900nm or so.

Subsequently, as illustrated in FIG. 23, a resist film 29 for sourcecontact hole formation is formed over the front surface 1 a of thesemiconductor wafer 1. Using this resist film as a mask, a sourcecontact hole 20, a chip edge opening, and the like are formed by dryetching. Subsequently, the resist film 29 that became unnecessary isentirely removed.

Subsequently, as illustrated in FIG. 24, the substrate front surface isetched (to, for example, the depth of 0.3 micrometers or so) byanisotropic dry etching using the patterned interlayer insulating film17 as a mask to form a recess region 32. Subsequently, ion implantationis carried out in this recess region 32 to form the p⁺-type body contactregion 18 and the outermost peripheral p⁺-type region 7. An example ofthe conditions for this ion implantation is as follows: dopant: BF₂;implantation energy: 30 keV or so; and dose amount: the order of10¹⁵/cm².

Subsequently, as illustrated in FIG. 25, an aluminum metal layer isformed by sputtering or the like through a barrier metal film of TiW orthe like and patterned. The metal source electrode 5, the guard ringelectrode 3, and the like are thereby formed.

Thereafter, a final passivation film such as inorganic final passivationfilm or organic inorganic final passivation film is formed thereover ifnecessary and a pad opening and a gate opening are formed. As the finalpassivation film, the following measure may be taken aside from such asingle-layer film as inorganic final passivation film or organicinorganic final passivation film: an organic inorganic final passivationfilm or the like is laminated over an inorganic final passivation filmlocated below.

3. Description of a First Modification (Double Line Wide Column Type) toa Plan Layout of the Device Structure of a Power MOSFET as an Example ofa Semiconductor Device in the First Embodiment of the Invention (MainlyFIG. 26 to FIG. 28)

In this section, description will be given to a modification to a planlayout in the embodiment described in sections above.

FIG. 26 (corresponding to FIG. 3) is an enlarged plan view of the chipcorner portion CR in FIG. 2 corresponding to FIG. 3. This drawingrelates to a first modification (double line wide column type) to a planlayout of the device structure of a power MOSFET as an example of asemiconductor device in the first embodiment of the invention. FIG. 27(corresponding to FIG. 4) is a device sectional view corresponding tothe section taken along line A-A′ of FIG. 26. FIG. 28 (corresponding toFIG. 5) is a device sectional view corresponding to the section takenalong line B-B′ of FIG. 26. Description will be given to the firstmodification (double line wide column type) to a plan layout of thedevice structure of a power MOSFET as an example of a semiconductordevice in the first embodiment of the invention with reference to thesedrawings.

As illustrated in FIG. 26 to FIG. 28, this modification is different inthat the p-type column region 9 b substantially surrounding the activecell region 6 and the first superjunction structure 41 is doubled. Themodification is identical in the other respects.

4. Description of a Second Modification (Single Coupled Wide ColumnType) to a Plan Layout of the Device Structure of a Power MOSFET as anExample of a Semiconductor Device in the First Embodiment of theInvention (Mainly FIG. 29)

In this section, description will be given to a modification to a planlayout in the embodiment described in sections above.

FIG. 29 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a second modification(single coupled wide column type) to a plan layout of the devicestructure of a power MOSFET as an example of a semiconductor device inthe first embodiment of the invention. Description will be given to thesecond modification (single coupled wide column type) to a plan layoutof the device structure of a power MOSFET as an example of asemiconductor device in the first embodiment of the invention withreference to this drawing.

As illustrated in FIG. 29, this modification is different from theexample in FIG. 3 in that the following are coupled to form multipleconcentric rectangular frame-like bodies: some of the ordinary p-typecolumn regions 9 a comprising the second superjunction structure 42 andall of the ordinary p-type column regions 9 a comprising the thirdsuperjunction structure 43. Therefore, the wide p-type column regions 9b above and below the active cell region 6 comprise each side of theinnermost rectangular frame-like body.

5. Description of a Third Modification (Double Coupled Wide Column Type)to a Plan Layout of the Device Structure of a Power MOSFET as an Exampleof a Semiconductor Device in the First Embodiment of the Invention(Mainly FIG. 30)

In this section, description will be given to a modification to a planlayout in the embodiment described in sections above.

FIG. 30 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a third modification(double coupled wide column type) to a plan layout of the devicestructure of a power MOSFET as an example of a semiconductor device inthe first embodiment of the invention. Description will be given to thethird modification (double coupled wide column type) to a plan layout ofthe device structure of a power MOSFET as an example of a semiconductordevice in the first embodiment of the invention.

As illustrated in FIG. 30, this modification is different from theexample in FIG. 29 in that: the entire rectangular frame-like bodycomprising the second superjunction structure 42 is a wide p-type columnregion 9 b; the upper and lower sides of the rectangular frame-like bodylocated outside it are wide p-type column regions 9 b; and they comprisea double coupled wide column as a whole. In this example, therectangular frame-like p-type column region partly wide is formed bycoupling together a wide p-type column region 9 b and an ordinary p-typecolumn region 9 a. Therefore, the narrow parts of the rectangularframe-like p-type column region partly wide are substantially identicalin width with the ordinary p-type column regions 9 a comprising thefirst superjunction structure 41.

6. Description of a Fourth Modification (Single Break Line Wide ColumnType) to a Plan Layout of the Device Structure of a Power MOSFET as anExample of a Semiconductor Device in the First Embodiment of theInvention (Mainly FIG. 31)

In this section, description will be given to a modification to a planlayout in the embodiment described in sections above.

FIG. 31 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a fourth modification(single break line wide column type) to a plan layout of the devicestructure of a power MOSFET as an example of a semiconductor device inthe first embodiment of the invention. Description will be given to thefourth modification (single break line wide column type) to a planlayout of the device structure of a power MOSFET as an example of asemiconductor device in the first embodiment of the invention.

As illustrated in FIG. 31, this modification is different from theexample in FIG. 3 in that the symmetric property of the chip cornerportions is enhanced by taking the following measure: the lengths of theordinary p-type column regions 9 a and the wide p-type column regions 9b comprising the second superjunction structure 42 and the thirdsuperjunction structure 43 are adjusted. That is, the linear p-typecolumn regions 9 (9 a, 9 b) are laid out by substantially symmetricallyarranging them.

7. Description of a Fifth Modification (Single Break Line Wide ColumnType with Auxiliary Column) to a Plan Layout of the Device Structure ofa Power MOSFET as an Example of a Semiconductor Device in the FirstEmbodiment of the Invention (Mainly FIG. 32)

In this section, description will be given to a modification to a planlayout in the embodiment described in sections above.

FIG. 32 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a fifth modification(single break line wide column type with auxiliary column) to a planlayout of the device structure of a power MOSFET as an example of asemiconductor device in the first embodiment of the invention.Description will be given to the fifth modification (single break linewide column type with auxiliary column) to a plan layout of the devicestructure of a power MOSFET as an example of a semiconductor device inthe first embodiment of the invention.

As illustrated in FIG. 32, this modification is characterized in that:the corner portion of the rectangular frame-like body in FIG. 31 is cutand placed inside and the symmetrical property of the chip cornerportion is further enhanced. (This makes it possible to maintainfavorable charge balance at corner portions.)

8. Description of the Device Structure (Basic Structure: Single PartlyHigh Concentration Column Type) of a Power MOSFET as an Example of aSemiconductor Device in a Second Embodiment of the Invention (Mainly,FIG. 33 and FIG. 35 to FIG. 37)

In Sections 8 to 10, description will be given to a device and the likeformed by a multi-epitaxy process. This device and the like aredifferent in the manufacturing process for superjunction structures andthe attributes of extraordinary p-type column regions. However, they aresubstantially identical in other common cross section structures and thelayout of p-type column regions. (In Sections 8 to 10, the extraordinaryp-type column regions are p-type column regions 52 p havingconcentration change due to ion implantation (or having change inwidth).)

FIG. 33 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawing relatesto the device structure (basic structure: single partly highconcentration column type) of a power MOSFET as an example of asemiconductor device in the second embodiment of the invention. FIG. 35is an impurity distribution chart of the p-type column region 51 puniform in concentration in the direction of depth related to thesection taken along line D-D′ of FIG. 33 or FIG. 34. (The impuritydistribution of an adjacent n-type column region 10 is also shown forthe purpose of comparison.) FIG. 36 is a first example (substantiallystepwise distribution) of an impurity distribution chart of the p-typecolumn region 52 p partly high in concentration in the direction ofdepth related to the section taken along line C-C′ of FIG. 33 or FIG.34. (The impurity distribution of an adjacent n-type column region 10 isalso shown for the purpose of comparison.) FIG. 37 is, a second example(substantially monotone increasing) of an impurity distribution chart ofthe p-type column region 52 p partly high in concentration in thedirection of depth related to the section taken along line C-C′ of FIG.33 or FIG. 34. (The impurity distribution of an adjacent n-type columnregion 10 is also shown for the purpose of comparison.) Description willbe given to the device structure (basic structure: single partly highconcentration column type) of a power MOSFET as an example of asemiconductor device in the second embodiment of the invention.

As illustrated in FIG. 33 (corresponding to FIG. 4), the devicestructure in the second embodiment corresponds to the basic structure ofthe first embodiment. It is different in the manufacturing process forsuperjunction structures and in that: as an extraordinary p-type columnregion, there is provided a p-type column region 52 p partly higher inconcentration than the ordinary-concentration p-type column regions 51p, not a wide p-type column region 9 b. In this example, the p-typecolumn region 51 p and the p-type column region 52 p are substantiallyidentical in width. (This is the same with the example in FIG. 34.)

FIG. 35 shows the p-type impurity concentration distribution of the D-D′section (FIG. 33 or FIG. 34) of the p-type column region 51 p portionuniform in concentration. (The n-type impurity concentrationdistribution of an adjacent n-type column region 10 is also shown forthe purpose of comparison.) It is preferred that the p-type impurityconcentration distribution of the C-C′ section of the p-type columnregion 52 p partly high in concentration in FIG. 33 or FIG. 34 should beas shown in FIG. 36 or FIG. 37. (The n-type impurity concentrationdistribution of an adjacent n-type column region 10 is also shown forthe purpose of comparison.) That is, it desirable that the followingshould be implemented when the p-type column region 51 p uniform inconcentration of the active cell region 6 and the chip peripheral region15 is at a reference concentration: the concentration of the lower partis higher than the reference concentration and the concentration of theupper part is lower than the reference concentration. This is intendedto implement the following as shown in FIG. 6: the distribution of thetotal charge amount Qn of n-type columns and that of the total chargeamount Qp of p-type columns are caused to intersect with each other inthe internal region of the drift region 30; and the electric fieldstrength is thereby maximized in the internal region away from the frontsurface. In multi-epitaxy techniques, upper and lower element columnsare coupled together by diffusion. Therefore, when the lower part is ata high concentration as shown in FIG. 36 and FIG. 37, that brings aboutan advantage that the optimum distribution is more easily generated.

9. Description of a First Modification (Double High Concentration ColumnType) to a Plan Layout of the Device Structure of a Power MOSFET as anExample of a Semiconductor Device in the Second Embodiment of theInvention (Mainly FIG. 34)

FIG. 34 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawing relatesto a first modification (double partly high concentration column type)to a plan layout of the device structure of a power MOSFET as an exampleof a semiconductor device in the second embodiment of the invention.Description will be given to the first modification (double highconcentration column type) to a plan layout of the device structure of apower MOSFET as an example of a semiconductor device in the secondembodiment of the invention with reference to this drawing.

As illustrated in FIG. 34 (corresponding to FIG. 4), the devicestructure of the second embodiment (first modification) corresponds tothe structure of the first embodiment illustrated in FIG. 26 to FIG. 28.It is different in the manufacturing process for superjunctionstructures and in that: as an extraordinary p-type column region, thereis provided a p-type column region 52 p partly higher in concentrationthan the p-type column region 51 p uniform in concentration, not a widep-type column region 9 b. This embodiment is exactly the same as inSection 9 in the other respects and the description thereof will not berepeated.

In the description up to this point, cases where extraordinary columns(for example, partly high-concentration column type, wide column, andthe like) are singly or doubly arranged have been taken as examples.They may be so structured that the number of them is larger depending onthe relation with dimensions, needless to add.

10. Description of the Wafer Process (Mainly by a Multi-EpitaxyTechnique) in a Manufacturing Method for a Semiconductor Device in theSecond Embodiment of the Invention (Basic Structure Taken as an Example)(Mainly FIG. 38 to FIG. 41 and FIG. 70 to FIG. 73)

In this section, description will be given to process stepscorresponding to the structure in FIG. 33. These process steps arebasically the same for the structure in FIG. 34 and other structures.The process steps in FIG. 14 to FIG. 25 are basically the same as theprocess steps in FIG. 41 and the following drawings. Therefore, only adifference will be described here. Concrete description will be givenwith the impurity profile in FIG. 37 taken as an example. The impurityprofile may be that in FIG. 36 or those obtained by turning theseimpurity profiles upside down. However, the impurity profiles shown inFIG. 36 and FIG. 37 bring about an advantage of stable process.

(1) Multiple Implantation Technique (Mainly FIG. 38 to FIG. 41)

FIG. 38 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice (the basic structure in FIG. 33 taken as an example) in thesecond embodiment of the invention (step of forming first-tier n-typesilicon epitaxial layer in multi-epitaxial growth). FIG. 39 illustratesa device section in the wafer process (mainly by a multi-epitaxytechnique) in a manufacturing method for a semiconductor device (thebasic structure in FIG. 33 taken as an example) in the second embodimentof the invention (step #1 of p-type impurity implantation in first-tiern-type silicon epitaxial layer in multi-epitaxial growth). FIG. 40illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method for a semiconductordevice (the basic structure in FIG. 33 taken as an example) in thesecond embodiment of the invention (step #2 of p-type impurityimplantation in first-tier n-type silicon epitaxial layer inmulti-epitaxial growth). FIG. 41 illustrates a device section in thewafer process (mainly by a multi-epitaxy technique) in a manufacturingmethod for a semiconductor device (the basic structure in FIG. 33 takenas an example) in the second embodiment of the invention (at the time ofmulti-epitaxial growth by a multi-epitaxy technique and the completionof final ion implantation). Description will be given to the waferprocess (mainly by a multi-epitaxy technique) in a manufacturing methodfor a semiconductor device (basic structure taken as an example) in thesecond embodiment of the invention with reference to these drawings.

First, as illustrated in FIG. 38, a first-tier n-type silicon epitaxiallayer 51 n 1 by multi-epitaxial growth, for example, 8 micrometers or sois formed on the front surface 1 a side of an n⁺-type single crystalsilicon wafer 1 s.

Subsequently, as illustrated in FIG. 39, a resist film 53 for ionimplantation is applied to the first-tier n-type silicon epitaxial layer51 n 1 and is patterned by lithography. Using the patterned resist film53 for ion implantation as a mask, impurity ions corresponding toordinary concentration is implanted in the first-tier p-type columnregion 51 p 1 of ordinary concentration and the first-tier p-type columnregion 52 p 1 of high concentration (first ion implantation).Thereafter, the resist film 53 for ion implantation that becameunnecessary is removed. Subsequently, a resist film 54 for ionimplantation is applied to the first-tier n-type silicon epitaxial layer51 n 1 again and is patterned by lithography. Using the patterned resistfilm 54 for ion implantation as a mask, impurity ions equivalent to thedifference between the concentration corresponding to the first-tierp-type column region 52 p 1 of high concentration and the first-tierp-type column region 51 p 1 of ordinary concentration are implanted(second ion implantation). Thereafter, the resist film 54 for ionimplantation that became unnecessary is removed.

Subsequently, similarly to FIG. 38, a second-tier n-type siliconepitaxial layer is formed and a resist film pattern 53 is formedthereover. Similarly to FIG. 39, the first ion implantation is carriedout and the pattern is replaced with the resist film pattern 54 again asillustrated in FIG. 40. Then the second ion implantation is carried out.To obtain such an impurity profile as shown in FIG. 37 at this time, anamount smaller than the dose amount in the second ion implantation forthe first tier is implanted.

This repetitive process is repeated more than once (for example, sixtimes) to obtain such a structure as illustrated in FIG. 41. In FIG. 41,the n-type silicon epitaxial layer 52 n at the time of completion ofmulti-epitaxial growth corresponds to the n-type column regions 10 inFIG. 14.

This state is equivalent to the state in FIG. 14; therefore, thefollowing process steps are the same as those in FIG. 14 and thefollowing drawings.

(2) Implantation Width Varying Technique (Mainly FIG. 70 to FIG. 73)

The difference between this example and the example in (1) above isdescribed below. In the example in (1), ion implantation is carried outin two steps for each multi-epitaxy layer. In this example, meanwhile,ion implantation is carried out once for each multi-epitaxy layer.Instead, the dose amount is changed by changing the area of openings ina resist pattern for ion implantation in extraordinary columns. Theformer is advantageous to the accurate control of dose amount and thelatter brings about an advantage of a halved number of times of ionimplantation.

FIG. 70 illustrates a device section in the wafer process (mainly by amulti-epitaxy technique) in a manufacturing method (modification) for asemiconductor device in the second embodiment of the invention (step offorming first-tier n-type silicon epitaxial layer in multi-epitaxialgrowth). (The basic structure in FIG. 33 and the doping profile in FIG.37 are taken as an example.) FIG. 71 illustrates a device section in thewafer process (mainly by a multi-epitaxy technique) in a manufacturingmethod (modification) for a semiconductor device in the secondembodiment of the invention (step #1 of p-type impurity implantation infirst-tier n-type silicon epitaxial layer in multi-epitaxial growth).(The basic structure in FIG. 33 and the doping profile in FIG. 37 aretaken as an example.) FIG. 72 illustrates a device section in the waferprocess (mainly by a multi-epitaxy technique) in a manufacturing method(modification) for a semiconductor device in the second embodiment ofthe invention (step of forming resist pattern for p-type impurityimplantation in second-tier n-type silicon epitaxial layer inmulti-epitaxial growth). (The basic structure in FIG. 33 and the dopingprofile in FIG. 37 are taken as an example.) FIG. 73 illustrates adevice section in the wafer process (mainly by a multi-epitaxytechnique) in a manufacturing method (modification) for a semiconductordevice in the second embodiment of the invention (at the time ofcompletion of p-type impurity implantation in second-tier n-type siliconepitaxial layer in multi-epitaxial growth and resist removal). (Thebasic structure in FIG. 33 and the doping profile in FIG. 37 are takenas an example.)

First, the processing illustrated in FIG. 70 is carried out similarly to(1) above. That is, a first-tier n-type silicon epitaxial layer 51 n 1by multi-epitaxial growth, for example, 8 micrometers or so is formed onthe front surface 1 a side of the n⁺-type single crystal silicon wafer 1s.

Subsequently, as illustrated in FIG. 71, a resist film 53 for ionimplantation is applied to the first-tier n-type silicon epitaxial layer51 n 1 and is patterned by lithography. At this time, the opening widthL2 of an opening for ion implantation for the extraordinary p-typecolumn is made larger than the opening width L1 of an opening for ionimplantation for the ordinary p-type column.

Subsequently, using the patterned resist film 53 for ion implantation asa mask, impurity ions corresponding to ordinary concentration isimplanted in the first-tier p-type column region 51 p 1 of ordinaryconcentration and the first-tier p-type column region 52 p 1 of highconcentration. Thereafter, the resist film 53 for ion implantation thatbecame unnecessary is removed.

Subsequently, the processing illustrated in FIG. 72 is carried out. Thatis, a second-tier n-type silicon epitaxial layer 51 n 2 is formedsimilarly to FIG. 71; a resist film pattern 53 is formed thereover; ionimplantation is carried out similarly to FIG. 71; and the resist film 53that became unnecessary is removed. Thus the state illustrated in FIG.73 is established. At this time, the opening width L2′ of an opening forion implantation for the extraordinary p-type column is so set that thefollowing is implemented: it is larger than the opening width L1 of anopening for ion implantation for the ordinary p-type column and slightlysmaller than the opening width L2 (FIG. 71) of an opening for ionimplantation for the extraordinary p-type column. As a result, thefollowing dose amount of the wide second-tier p-type column region 52 p2 in ion implantation is obtained: a dose amount larger than the doseamount of the second-tier p-type column region 51 p 2 uniform inconcentration in ion implantation and slightly smaller than the doseamount of the wide first-tier p-type column region 52 p 1 in ionimplantation.

This repetitive process is repeated more than once (for example, sixtimes) to obtain such a structure as illustrated in FIG. 41.

11. Description of a Modification (Trench Gate) to the Gate Structure ofa Power MOSFET as an Example of a Semiconductor Device (Basic Structureand the Like) in the First Embodiment of the Invention (Mainly FIG. 43)

In this section, a trench gate will be described as a modification tothe gate structure of the first embodiment. It is believed that trenchvertical power MOSFETs having a superjunction are effective mainly todevices with a source-drain breakdown voltage of 100 volts to 300 voltsor so. In the following description, therefore, devices with asource-drain breakdown voltage of 200 volts or so will be taken as anexample.

FIG. 43 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawing relatesto a modification (trench gate) to the gate structure of a power MOSFETas an example of a semiconductor device (basic structure and the like)in the first embodiment of the invention. Description will be given tothe modification (trench gate) to the gate structure of a power MOSFETas an example of a semiconductor device (basic structure and the like)in the first embodiment of the invention with reference to this drawing.

In this example, as illustrated in FIG. 43, a linear polysilicon gateelectrode 11 is buried in a gate trench (linear groove for gate) with agate insulating film 21 in between. This trench gate structure bringsabout an advantage that low on resistance can be easily achieved ascompared with planar structures. Meanwhile, it is disadvantageous inachieving a source-drain breakdown voltage on the order of 500 to 600volts as compared with planar structures.

The elements other than the gate portion are the same as described up tothis point in relation to the first embodiment and the descriptionthereof will not be repeated.

12. Description of the Device Structure (n/n-Multilayer Ordinary EpitaxyType) of a Power MOSFET as an Example of a Semiconductor Device in theThird Embodiment of the Invention (Mainly FIG. 42, FIG. 44, and FIG. 45)

In the above examples, the source-drain breakdown voltage of a device isenhanced and other like purposes are accomplished by taking thefollowing measure: the width of extraordinary p-type column regions 9 b,52 p in an end area of the active cell region 6 or the concentrationthereof is increased to locally operate charge balance; and electricfield concentration is thereby prevented from occurring in a surfaceregion in proximity to such extraordinary p-type column regions 9 b, 52p. In the example described below, the source-drain breakdown voltage ofa device is enhanced and other like purposes are accomplished by takingthe following measure: based mainly on an epitaxy trench fillingtechnique, an n-type silicon epitaxial layer 1 n (ordinary epitaxy layeror base epitaxy layer) as a base for forming a superjunction ismulti-stratified. Description will be given to a method for this.

FIG. 44 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawing relatesto the device structure (n/n-multilayer ordinary epitaxy type) of apower MOSFET as an example of a semiconductor device in the thirdembodiment of the invention. FIG. 45 is an explanatory drawing showingthe relation between charge balance in the direction of depth andbreakdown voltage in the superjunction in FIG. 44. FIG. 42 is anexplanatory drawing schematically illustrating the relation betweenbreakdown voltage and charge unbalance observed in case of the n-typeepitaxial structure (n/n-multilayer ordinary epitaxy structure) in FIG.44 and a common single ordinary epitaxial structure. Description will begiven to the device structure (n/n-multilayer ordinary epitaxy type) ofa power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention with reference to these drawings.

FIG. 44 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3. As illustrated in FIG. 44, the semiconductorsubstrate 1 in which this device is formed is obtained by forming thefollowing epitaxy layer over an n⁺-type single crystal silicon substrateis (on the back surface 1 b side of the semiconductor substrate 1): atwo-layer ordinary epitaxy layer 1 n comprised of an n-type lowersilicon epitaxial layer 1 t and an n-type upper silicon epitaxial layer1 d. Therefore, an n-type upper column region 10 d comprising an n-typecolumn region 10 is part of the n-type upper silicon epitaxial layer 1d; and similarly, an n-type lower column region lot comprising an n-typecolumn region 10 is part of the n-type lower silicon epitaxial layer 1t. A field insulating film 16 and a gate insulating film 21 are providedon the front surface 1 a side of the semiconductor substrate 1 and apolysilicon gate electrode 11 is provided over the gate insulating film21. An interlayer insulating film 17 is provided so that it covers thefield insulating film 16 and the polysilicon gate electrode 11. In thesurface region on the front surface 1 a side of the semiconductorsubstrate 1, there is provided an n⁺-type source region 19 formed in aself-aligned manner with respect to the polysilicon gate electrode 11.(An n⁺-type channel stopper region 8 is usually formed at the same timeas this step.) In the surface region on the front surface 1 a side ofthe semiconductor substrate 1, there is provided a p⁺-type body contactregion 18 in correspondence with a contact hole formed in the interlayerinsulating film 17 in the vicinity of the polysilicon gate electrode 11.The outermost peripheral p⁺-type region 7 is usually formed at the sametime as this step. Further, a guard ring 3, a source metal electrode 5,and the like comprised of a barrier metal film, an aluminum metalelectrode film, or the like are formed over the interlayer insulatingfilm 17. The area ranging from the outer half part of the p-type bodyregion 12 p(12) at an end of the active cell region 6 to the outer endportion of a field plate part 13 is the intermediate region 40. The arealocated outside the above area is the cell peripheral region 15.

FIG. 45 illustrates the electrical structure of the semiconductorsubstrate 1 in the superjunction structure in FIG. 44. In FIG. 45, thearea on the left side indicates charge distribution (half pitch of acycle period) and the area located on the right side indicates electricfield strength distribution. (The electric field strength distributionis equivalent to the absolute values of electric field strength inproximity to the border between a p-type column region 9 and an n-typecolumn region 10 and in proximity to its extended line.) As indicated inFIG. 45, in actuality, the width of the p-type column region 9 is oftenin a tapered shape and it is slightly reduced as it goes downward.Conversely, the width of an n-type column region 10 is often in atapered shape and is slightly reduced as it goes upward. As a result,the distribution of donor and the distribution of acceptor in theminimum symmetrical unit region (left side of FIG. 45) between thefollowing vertical center planes is as shown on the left side of FIG.45: the vertical center plane of the p-type column region 9 as asymmetry plane and the vertical center plane of the n-type column region10 in proximity thereto. (The area of the portion surrounded by thepolygonal line and the y-axis is equivalent to the total quantity Qn ofdonor and the total quantity Qp of acceptor.) That is, it is understoodthat there are two points at which charge balance can be accuratelyheld. In correspondence therewith, two maximum points (apexes) appear inthe distribution of electric field strength E in correspondence withthese two points as shown on the right side of FIG. 45. For this reason,the source-drain breakdown voltage V_(B) (the area surrounded by thepolygonal line and the y-axis) can be enhanced as compared with caseswhere there is one apex (that is, cases where the n-type column region10 is comprised of one concentration region).

This will be considered with respect to the outer end portion of theactive cell region 6 or the intermediate region 40. Multiple points atwhich charge balance is held are formed in the interior portion, not inthe front surface, without fail; therefore, electric field concentrationin the surface region can be avoided. FIG. 42 illustrates the relationbetween local charge balance and source-drain breakdown voltage based oncomparison of a case of ordinary single epitaxial layer structure with acase of two-layer structure in this example. As shown in FIG. 42, thestructure described in this section delivers high breakdown voltage overa relatively wide charge unbalance range.

13. Description of a Manufacturing Process (Mainly by an Epitaxy TrenchFilling Technique) for the Device Structure (n/n-Multilayer OrdinaryEpitaxy Type) of a Power MOSFET as an Example of a Semiconductor Devicein the Third Embodiment of the Invention (Mainly FIG. 46 to FIG. 60)

In this section, description will be given to a substantial part ofwafer process with the device section in FIG. 44 taken as an example.This process can also be applied to device structures described in thefollowing sections substantially without change, except somedifferences.

FIG. 46 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawingillustrates a manufacturing process (mainly by an epitaxy trench fillingtechnique) related to the device structure (n/n-multilayer ordinaryepitaxy type) of a power MOSFET as an example of a semiconductor devicein the third embodiment of the invention (step of patterning hard maskfilm for forming p-type column groove). FIG. 47 is a device sectionalview corresponding to the section taken along line A-A′ of FIG. 3corresponding to FIG. 4. This drawing illustrates a manufacturingprocess (mainly by an epitaxy trench filling technique) related to thedevice structure (n/n-multilayer ordinary epitaxy type) of a powerMOSFET as an example of a semiconductor device in the third embodimentof the invention (p-type column groove etching step). FIG. 48 is adevice sectional view corresponding to the section taken along line A-A′of FIG. 3 corresponding to FIG. 4. The drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (epitaxy trench filling step). FIG. 49 is adevice sectional view corresponding to the section taken along line A-A′of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (planarization step). FIG. 50 is a devicesectional view corresponding to the section taken along line A-A′ ofFIG. 3 corresponding to FIG. 4. This drawing illustrates a manufacturingprocess (mainly by an epitaxy trench filling technique) related to thedevice structure (n/n-multilayer ordinary epitaxy type) of a powerMOSFET as an example of a semiconductor device in the third embodimentof the invention (p⁻-type RESURF region introduction step). FIG. 51 is adevice sectional view corresponding to the section taken along line A-A′of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (field insulating film etching step). FIG.52 is a device sectional view corresponding to the section taken alongline A-A′ of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (p-type body region introduction step). FIG.53 is a device sectional view corresponding to the section taken alongline A-A′ of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (gate oxidation step). FIG. 54 is a devicesectional view corresponding to the section taken along line A-A′ ofFIG. 3 corresponding to FIG. 4. This drawing illustrates a manufacturingprocess (mainly by an epitaxy trench filling technique) related to thedevice structure (n/n-multilayer ordinary epitaxy type) of a powerMOSFET as an example of a semiconductor device in the third embodimentof the invention (gate polysilicon film formation step). FIG. 55 is adevice sectional view corresponding to the section taken along line A-A′of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (gate polysilicon film patterning step).FIG. 56 is a device sectional view corresponding to the section takenalong line A-A′ of FIG. 3 corresponding to FIG. 4. This drawingillustrates a manufacturing process (mainly by an epitaxy trench fillingtechnique) related to the device structure (n/n-multilayer ordinaryepitaxy type) of a power MOSFET as an example of a semiconductor devicein the third embodiment of the invention (n⁺-type source regionintroduction step). FIG. 57 is a device sectional view corresponding tothe section taken alone line A-A′ of FIG. 3 corresponding to FIG. 4.This drawing illustrates a manufacturing process (mainly by an epitaxytrench filling technique) related to the device structure(n/n-multilayer ordinary epitaxy type) of a power MOSFET as an exampleof a semiconductor device in the third embodiment of the invention(interlayer insulating film formation step). FIG. 58 is device sectionalview corresponding to the section taken along line A-A′ of FIG. 3corresponding to FIG. 4. This drawing illustrates a manufacturingprocess (mainly by an epitaxy trench filling technique) related to thedevice structure (n/n-multilayer ordinary epitaxy type) of a powerMOSFET as an example of a semiconductor device in the third embodimentof the invention (contact hole formation step). FIG. 59 is a devicesectional view corresponding to the section taken along line A-A′ ofFIG. 3 corresponding to FIG. 4. This drawing illustrates a manufacturingprocess (mainly by an epitaxy trench filling technique) related to thedevice structure (n/n-multilayer ordinary epitaxy type) of a powerMOSFET as an example of a semiconductor device in the third embodimentof the invention (p⁺-type body contact region introduction step). FIG.60 is a device sectional view corresponding to the section taken alongline A-A′ of FIG. 3 corresponding to FIG. 4. This drawing illustrates amanufacturing process (mainly by an epitaxy trench filling technique)related to the device structure (n/n-multilayer ordinary epitaxy type)of a power MOSFET as an example of a semiconductor device in the thirdembodiment of the invention (aluminum metal electrode formation step).Description will be given to a manufacturing process (mainly by anepitaxy trench filling technique) for the device structure(n/n-multilayer ordinary epitaxy type) of a power MOSFET as an exampleof a semiconductor device in the third embodiment of the invention withreference to these drawings.

First, the processing described in Section 2 is carried out asillustrated in FIG. 46. That is, a semiconductor wafer 1 in which ann-epitaxial layer in, 50 micrometers or so in thickness, doped withphosphorus is formed over an n⁺-silicon single crystal substrate 1 sdoped with antimony is prepared. (Antimony is doped to the order of, forexample, 10¹⁸ to 10¹⁹/cm³.) (In this example, the n⁺-silicon singlecrystal substrate 1 s is, for example, a 200φ-wafer. The wafer diametermay be 150φ, 300φ, or 450φ.) (In terms of device, the n-epitaxial layerin is a region to be a drift region and the concentration is, forexample, the order of 10¹⁵/cm³ or so. More specific description will begiven. When the thickness of the n-type lower silicon epitaxial layer itis 20 micrometers or so and its phosphorus concentration is 3×10¹⁵/cm³or so, the n-type upper silicon epitaxial layer 1 d is so set that thefollowing is implemented: its thickness is 30 micrometers or so and itsphosphorus concentration is 2.5×10¹⁵/cm³ or so.) A hard mask film 22 forforming trenches for p-type columns comprised of, for example, P-TEOS(Plasma-Tetraethylorthosilicate) or the like is formed over the devicesurface 1 a (main surface on the opposite side to the back surface 1 b)of the semiconductor wafer 1. The width Wn of the n-type column regionat the patterning level is, for example, 6 micrometers or so and thewidth Wp of the p-type column region is, for example, 4 micrometers orso. (That is, the pitch of the superjunction is 10 micrometers or so.)

Subsequently, as illustrated in FIG. 47, the n-epitaxial layer 1 n andthe like are subjected to anisotropic dry etching with the hard maskfilm 22 for forming trenches for p-type columns used as a mask. (Thehard mask film 22 is, for example, a plasma TEOS film, a silicon nitridefilm, or a laminated film of them and an example of its thickness is 1.5micrometers or so.) (An example of the gas atmosphere is a mixedatmosphere of Ar, SF₆, O₂, and the like and an example of the etchingdepth is 50 micrometers or so.) Trenches 23 for p-type columns arethereby formed. Subsequently, the hard mask film 22 that becameunnecessary is removed.

Subsequently, as illustrated in FIG. 48, burying epitaxial growth iscarried out on the trenches 23 for p-type columns to form a p-typeburying epitaxial layer 24. (The boron concentration is, for example,5×10¹⁵/cm³ or so.) Examples of the source gas for burying epitaxialgrowth are silicon tetrachloride, trichlorosilane, dichlorosilane, andmonosilane. An example of the preferable range of processing atmosphericpressure is 10 kPa to 110 kPa or so.

Subsequently, as illustrated in FIG. 49, the p-type burying epitaxiallayer 24 located outside the trenches 23 for p-type columns is removedby a planarization step, for example, CMP (Chemical MechanicalPolishing). Then the front surface 1 a of the semiconductor wafer 1 isplanarized.

Substantially, as illustrated in FIG. 50, a silicon oxide film 16 isformed over substantially the entire front surface 1 a of thesemiconductor wafer 1 by thermal oxidation. (The silicon oxide film 16is a field oxide film and its thickness is, for example, 350 nm or so.)A resist film 25 for introducing a p⁻-type RESURF region is formedthereover by lithography. Subsequently, a p⁻-type surface RESURF region14 is introduced by ion implantation with the resist film 25 forintroducing a p⁻-type RESURF region used as a mask. (The dopant is, forexample, boron; the dose amount is, for example, 1×10¹¹ to 1×10¹²/cm² orso; and the implantation energy is, for example, 200 keV or so.)Thereafter, the resist film 25 that became unnecessary is entirelyremoved.

Subsequently, as illustrated in FIG. 51, a resist film 26 for fieldinsulating film processing is formed over the field oxide film 16 bylithography and using it as a mask, the edge portions, active cellregion 6, and the like of the chip are exposed. Thereafter, the resistfilm 26 that became unnecessary is entirely removed.

Subsequently, as illustrated in FIG. 52, a resist film 27 for p-typebody region introduction is formed over the front surface 1 a of thesemiconductor wafer 1 by lithography. Using this film as a mask, ap-type body region 12 is introduced by ion implantation (the dopant isboron). This ion implantation is carried out in two steps describedbelow, for example. At the first step, implantation is carried out at,for example, 200 keV on the order of 10¹³/cm² and the subsequent step,or the second step, implantation is carried out at, for example, 75 keVon the order of 10¹²/cm².

According to the non-self-alignment p-type body region introductionprocess used here, the portion to be a gate electrode has been alreadyrecessed to 1 micrometer or so at the time of doping. Therefore, it ispossible to reduce the burden on the subsequent heat treatment. As aresult, it is possible to reduce unwanted variation in the impuritydistribution of the superjunction. However, as the result of the depthof the p-type body region 12 being reduced, breakdown voltage may bereduced as a side-effect. To avoid this problem, the ion implantation inthe p-type body region 12 is carried out in two steps as mentionedabove.

As mentioned above, the p-type body region 12 of the second conductivitytype is introduced before the formation of a gate polysilicon film. Thusthe introduced portion is not limited by the width or position of thegate and it can be introduced in the optimum position. This makes itpossible to reduce the burden on the subsequent heat treatment and, inaddition, use the subsequent heat treatment (including the formation ofa gate polysilicon film and the like) in a shared manner. Thisnon-self-alignment p-type body region introduction process is applicableto not only cases where the ordinary epitaxy layer as the base forsuperjunction formation is of single layer but also cases where it is ofmultilayer.

Subsequently, as illustrated in FIG. 53, a gate oxide film 21 (forexample, 50 to 200 nm or so in film thickness) is formed over the frontsurface 1 a of the semiconductor wafer 1 by thermal oxidation (forexample, wet oxidation at 950 degrees Celsius).

As illustrated in FIG. 54, a gate polysilicon film 11 (for example, 200to 800 nm or so in film thickness) is formed over the gate oxide film 21by, for example, low pressure CVD (Chemical Vapor Deposition). As wafercleaning before gate oxidation, for example, wet cleaning using a firstcleaning liquid and a second cleaning liquid can be applied. The firstcleaning liquid is a liquid of ammonia:hydrogen peroxide:purewater=1:1:5 (volume ratio) and the second cleaning liquid is a liquid ofhydrochloric acid:hydrogen peroxide:pure water=1:1:6 (volume ratio).

Subsequently, as illustrated in FIG. 55, the gate electrode 11 ispatterned by dry etching.

Subsequently, as illustrated in FIG. 56, a resist film 28 for n⁺-sourceregion introduction is formed by lithography. Using this film as a mask,an n⁺-source region 19, the n⁺-type channel stopper region 8 of chipedge parts, and the like are introduced by ion implantation (forexample, arsenic). (The dopant is, for example, arsenic; the dose amountis, for example, the order of 10¹⁵/cm² or so; and the implantationenergy is, for example, 40 keV or so.) Thereafter, the resist film 28that became unnecessary is entirely removed.

Subsequently, as illustrated in FIG. 57, a PSG (Phospho-Silicate-Glass)film 17 (interlayer insulating film) is formed over substantially theentire front surface 1 a of the semiconductor wafer 1 by CVD or thelike. (An SOG film may be stacked above and planarized.) As theinterlayer insulating film 17, aside from the PSG film, BPSG, TEOS film,SiN film, others, or a composite film of them can be applied. An exampleof the total film thickness of the interlayer insulating film 17 is 900nm or so.

Subsequently, as illustrated in FIG. 58, a resist film 29 for sourcecontact hole formation is formed over the front surface 1 a of thesemiconductor wafer 1. Using this resist film as a mask, a sourcecontact hole 20, a chip edge opening, and the like are formed by dryetching. Subsequently, the resist film 29 that became unnecessary isentirely removed.

Subsequently, as illustrated in FIG. 59, the substrate front surface isetched (to, for example, the depth of 0.3 micrometers or so) byanisotropic dry etching using the patterned interlayer insulating film17 as a mask to form a recess region. Subsequently, ion implantation iscarried out in this recess region to form the p⁺-type body contactregion 18 and the outermost peripheral p⁺-type region 7. An example ofthe conditions for this ion implantation is as follows: dopant: BF₂;implantation energy: 30 keV or so; and dose amount: the order of10¹⁵/cm².

Subsequently, as illustrated in FIG. 60, an aluminum metal layer isformed by sputtering or the like through a barrier metal film of TiW orthe like and patterned. The metal source electrode 5, the guard ringelectrode 3, and the like are thereby formed.

Thereafter, a final passivation film such as inorganic final passivationfilm or organic inorganic final passivation film is formed thereover ifnecessary and a pad opening and a gate opening are formed. As the finalpassivation film, the following measure may be taken aside from such asingle-layer film as inorganic final passivation film or organicinorganic final passivation film: an organic inorganic final passivationfilm or the like is laminated over an inorganic final passivation filmlocated below.

14. Single Narrow n-Type Column (Mainly FIG. 64 to FIG. 66)

The examples in this section and the next section are respectivelymodifications to the examples of the layout of extraordinary p-typecolumns in Section 1 and Section 3. A difference from the layout ofextraordinary p-type columns is in that: in the examples in Sections 14and 15, an extraordinary n-type column is introduced in place of theextraordinary p-type column.

FIG. 64 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a sixth modification(narrow n-type column type: #1) to a plan layout of the device structureof a power MOSFET as an example of a semiconductor device in the firstembodiment of the invention. FIG. 65 is a device sectional viewcorresponding to the section taken along line A-A′ of FIG. 64. FIG. 66is a device sectional view corresponding to the section taken along lineB-B′ of FIG. 64.

As illustrated in FIG. 64 to FIG. 66, a first superjunction structure41, a second superjunction structure 42, and a third superjunctionstructure 43 are all comprised of an ordinary p-type column region 9 aas a rule. Then the width of the second superjunction structure 42 and ap-type column-p-type column region 61 (extraordinary n-type column andthe like) and a p-type column end-p-type column region 62 in proximitythereto is made smaller than the width between the ordinary p-typecolumns. As a result, it is possible to locally break down chargebalance and shift the high electric field portion from the surfaceregion to the bulk region located below by the same principle asdescribed with reference to FIG. 6. In this example, the width of p-typecolumn regions 9 a formed by an implant epitaxy process can be madeidentical. This brings about the following advantage: conditions for theimplant epitaxy process can be easily optimized as compared with caseswhere a p-type column region having an extraordinary width existstogether as in Section 1 and Section 3.

15. Double Narrow n-Type Column (Mainly FIG. 67 to FIG. 69)

FIG. 67 is an enlarged plan view of the chip corner portion CR in FIG. 2corresponding to FIG. 3. This drawing relates to a seventh modification(narrow n-type column type: #2) to a plan layout of the device structureof a power MOSFET as an example of a semiconductor device in the firstembodiment of the invention. FIG. 68 is a device sectional viewcorresponding to the section taken along line A-A′ of FIG. 67. FIG. 69is a device sectional view corresponding to the section taken along lineB-B′ of FIG. 67.

As illustrated in FIG. 67 to FIG. 69, extraordinary n-type columns andthe like are multiply arranged using a narrow p-type column end-p-typecolumn region 62, narrow p-type column-p-type column regions 61 a, 61 b,61 c, and the like. The features of Section 3 and the features ofSections 14 are provided together.

16. Description of Variations in Overall Column Layout (Layout of p-TypeColumn Regions) Common to Each Embodiment (Mainly FIG. 61 to FIG. 63)

FIG. 61 is a column overall layout diagram (basic layout) correspondingto FIG. 2. FIG. 62 is a column overall layout diagram of a firstmodification to FIG. 61. FIG. 63 is a column overall layout diagram of asecond modification to FIG. 61.

In the above description of each of the embodiments, the following casehas been taken as an example: a case where such a p-type column layoutas illustrated in FIG. 61 corresponding to FIG. 2 is used and theorientation 55 of the gate in the active cell region and the orientationof the p-type columns 9 are parallel to each other. However, theinvention is not limited to this and the gate orientation 56 may be usedand the overall column layout may be as illustrated in FIG. 62 or FIG.63.

17. Consideration of General and Each Embodiment and Summary

The present inventors repeated simulation based on such a full chiplayout (including peripheral termination) as illustrated in FIG. 2. Theresult of the simulation revealed that such an unwanted breakdown modeas shown on the left side of FIG. 10 was established due to subtlefluctuation in process parameter. That is, the following takes placewhen the dose amount of a p⁻-type surface RESURF region is shifted tothe smaller side in the border (intermediate region) between a cell endpart and a chip peripheral region: when charge balance in asuperjunction is shifted to Qp<Qn as a whole, electric fieldconcentration is prone to occur in proximity to the cell peripheral bodyregion and there is a possibility that the breakdown voltage of theentire device is degraded.

The following is a description of a gist of the remedial measuresagainst it, described up to this point:

-   (1) In the intermediate region, the width of at least some p-type    column region is increased by, for example, 10 to 40% or so as    compared with the principal p-type column regions in the other    regions. The charge balance at this portion is thereby made    substantially equivalent or Qp rich (that is, Qp=xQn; 1≦x≦1.3 or    so).-   (2) In the intermediate region, the impurity concentration of at    least some p-type column region is increased by, for example, 10 to    40% or so as compared with the principal p-type column regions in    the other regions. The charge balance at this portion is thereby    made substantially equivalent or Qp rich (that is, Qp=xQn; 1≦x≦1.3or    so).-   (3) In the entire superjunction structures, the n-type epitaxial    layers are provided with a multilayer structure in which the upper    part is higher in concentration. For example, the impurity    concentration of the upper part is relatively increased by, for    example, 10 to 40% or so as compared with the lower part. This makes    it possible to shift a maximum point of electric field strength in    the direction of depth to the depth of a column. As a result, the    concentration of electric field strength in the intermediate region    can be reduced.

Or, (4) Local ((1), (2), Section 11, and the like) or global ((3) andthe like) adjustment of charge balance having the same effect is carriedout.

The following is a description of the effect obtained by local measuresdescribed in (1), (2), and the like and the reasons for this:

-   (A) When Qp≧Qn, electric field strength distribution at the time of    avalanche breakdown has a peak in the direction of the depth of a    column and this reduces the electric field strength in the    superficial portion of the column. The reason for this is as    described below. The front surface of a p-column coupled with source    potential is at 0V. When Qp≧Qn, the p-column is less prone to be    depleted. As a result, the distance between equipotential lines of    the front surface of the p-column and the front surface of an    n-column adjacent thereto is increased. This weakens the electric    field strength at the column superficial portion.-   (B) The electric field at the outer end portion of the cell    peripheral body region is reduced by (A). The reason for this is as    described below. Equipotential lines terminated from the cell part    to the peripheral portion are wider in spacing on the cell part    front surface side. Therefore, the spacing between equipotential    lines in proximity to a p-type well corner portion (outer end    portion of the cell peripheral body region) is also increased and    this reduces the electric field at the p-type well corner portion.-   (C) Because of (B), breakdown voltage fluctuation due to variation    in the amount of ion implantation in a p⁻-type surface RESURF region    in the vicinity of the active cell region can be reduced. More    specific description will be given. When Qp<Qn and the spacing    between equipotential lines is narrow in proximity to the front    surface of the cell part, an electric field is prone to be    concentrated in proximity to a p-type well corner portion.    Therefore, the breakdown voltage of the device is sensitive to the    impurity concentration of the p-RESURF region. When Qp≧Qn, however,    the electric field in proximity to the p-type well corner portion    can be reduced. Therefore, the breakdown voltage of the device    becomes insensitive to the impurity concentration of the p-RESURF    region and variation in breakdown voltage can be suppressed.

18. End Summary

Up to this point, concrete description has been given to the inventionmade by the present inventors based on embodiments thereof. However, theinvention is not limited to these embodiments and can be variouslymodified without departing from the subject matter thereof, needless toadd.

Some examples will be taken. In the above concrete description of theembodiments, a MOS structure with a planar gate structure has been takenas an example. However, the invention is not limited to this and can beexactly similarly applied to trench gate structures such as U-MOSFET,needless to add. As the layout of MOSFET, a striped arrangement parallelto pn-columns has been taken as an example. However, the layout can bevariously modified and an arrangement orthogonal to pn-columns and alattice arrangement are also acceptable.

In the above concrete description of the embodiments, a case where ann-channel device is mainly formed over the upper surface of ann-epitaxial layer placed over an n⁺-silicon single crystal substrate hasbeen taken as an example. However, the invention is not limited to theseembodiments and a p-channel device may be formed over the upper surfaceof an n-epitaxial layer placed over a p⁺-silicon single crystalsubstrate.

In the above concrete description of the embodiments, a power MOSFET hasbeen taken as an example. However, the invention is not limited to theseembodiments and can also be applied to the following, needless to add:power devices, that is, diodes, bipolar transistors, IGBTs (Insulatedgate Bipolar Transistors), and the like having a superjunctionstructure. It is also applicable to semiconductor integrated circuitdevices and the like incorporating such a power MOSFET, a diode, abipolar transistor, IGBT, or the like, needless to add.

In the above concrete description of the embodiments, a trench filltechnique has been mainly taken as an example of a method for formingsuperjunction structures. However, the invention is not limited to theseembodiments and can also be applied to, for example, a multi-epitaxialtechnique and the like, needless to add.

In the above description, a case where a p-type column region is formedin an n-type region has been taken as an example of the structure of asuperjunction. Instead, an n-type column region may be formed in ap-type region, needless to add.

In the above description, an n-channel device has been mainly taken asan example. The examples taken up to this point can also be applied to ap-channel device substantially without change by pn inverting operation.

In the above description, type surface RESURF region, field plate, andthe like have been taken examples of means for reducing the electricfield concentration in a drift region front surface. In addition, afield limiting ring, a floating field ring, or the like may be usedtogether.

What is claims is:
 1. A method for manufacturing a semiconductor deviceincluding a power MISFET having a super junction structure, comprisingsteps of: (a) providing a semiconductor substrate; (b) forming a firstn-type layer over the semiconductor substrate; (c) selectivelyintroducing impurities into the first n-type layer, thereby formingfirst and second p-type impurity regions in the first n-type layer; (d)forming a second n-type layer over the first n-type layer, the firstp-type impurity region and the second p-type impurity region; (e)selectively introducing impurities into the second n-type layer, therebyforming third and fourth p-type impurity regions in the second n-typelayer such that the first and third p-type impurity regions areconnected and the second and fourth p-type impurity regions areconnected; (f) forming a body region of the power MISFET in the secondn-type layer such that the body region is connected to a first p-typecolumn and a second p-type column, (g) forming a source region of thepower MISFET in the body region; (h) forming a gate insulating film ofthe power MISFET over the second n-type layer; and (i) forming a gateelectrode of the power MISFET over the gate insulating film, wherein thefirst p-type column of the super junction structure comprises the firstand third p-type impurity regions and extends in a first direction in aplan view, wherein the second p-type column of the super junctionstructure comprises the second and fourth p-type impurity regions andextends in the first direction in the plan view, wherein the secondp-type column is arranged between the first p-type column and an edge ofthe semiconductor substrate in a second direction perpendicular to thefirst direction in the plan view, and wherein the second p-type columnincludes a larger impurity concentration portion than the first p-typecolumn.
 2. A method for manufacturing a semiconductor device accordingto the claim 1, wherein the step (c) includes the steps of: (c1) formingthe first and second p-type impurity regions by using a first resistfilm such that a part of the first n-type layer is exposed; and (c2)after the step (c1), selectively introducing impurities into the secondp-type impurity region by using a second resist film such that thesecond p-type impurity region is exposed and the first p-type impurityregion is covered.
 3. A method for manufacturing a semiconductor deviceaccording to the claim 2, wherein the step (e) includes the steps of:(e1) forming the third and fourth p-type impurity regions by using athird resist film such that a part of the second n-type layer isexposed; and (e2) after the step (e1), selectively introducingimpurities into the fourth p-type impurity region by using a fourthresist film such that the fourth p-type impurity region is exposed andthe third p-type impurity region is covered.
 4. A method formanufacturing a semiconductor device according to the claim 3, whereinthe second p-type impurity region includes a larger impurityconcentration than the fourth p-type impurity region.
 5. A method formanufacturing a semiconductor device according to the claim 4, whereinthe second p-type impurity region includes a larger impurityconcentration than each of the first, third and fourth p-type impurityregions.
 6. A method for manufacturing a semiconductor device accordingto the claim 1, wherein the first and second n-type layers are formed byepitaxial growth.